Enforcement Officer / Accounts Officer (EO/AO) 2020 recruitment test, advertisement 421. Transcribed from the Commission's own booklet (series A, NMJX-U-GTA); answer as per the official UPSC final answer key. This question is in Part A. Answer last reviewed 24 August 2026.

The car which went past us (a) | when we were driving on the highway (b) | must have been doing at least a hundred miles an hour. (c) | No error (d)

(a)The car which went past us
(b)when we were driving on the highway
(c)must have been doing at least a hundred miles an hour.
(d)No error

Answer

Why

Correct — D, (d) No error.

The sentence is ‘The car which went past us when we were driving on the highway must have been doing at least a hundred miles an hour.’ Read segment by segment, every part of it is sound, so the answer is the separate ‘No error’ choice.

Segment (a): ‘which’ is the right relative pronoun for a thing, and ‘went past us’ is right too. ‘Past’ here is the preposition meaning ‘by, beyond’, and it is what follows the verb ‘go’ — go past, drive past, walk past. The word a candidate half-expects to see is ‘passed’, the past tense of the verb ‘to pass’, but ‘went passed’ would be two verbs in a row and is never English. Either ‘the car which went past us’ or ‘the car which passed us’ would do; the sentence has chosen the first and executed it correctly.

Segment (b): ‘when we were driving on the highway’ sets a longer action already in progress against which the shorter action of segment (a) happened, which is exactly what the past continuous is for. The pairing of a simple past for the brief event and a past continuous for the surrounding situation is the standard English arrangement — the phone rang while I was cooking. ‘On the highway’ is the ordinary preposition for a road one is travelling along.

Segment (c): ‘must have been doing’ is a deduction, not an obligation. This is the epistemic use of ‘must’ — the speaker did not see the speedometer, but infers a near-certain conclusion about the past from the evidence of the car flashing by. Since the conclusion is about an action in progress at that past moment, the form needed is ‘must have been’ plus the -ing participle, and that is what is printed. ‘Doing a hundred miles an hour’ is idiomatic for travelling at that speed, ‘at least’ correctly marks a lower bound, and ‘an hour’ takes ‘an’ because ‘hour’ opens with a silent h and therefore with a vowel sound. Nothing here needs correcting.

Why the others are wrong

(a)The car which went past us — This part contains no error, so marking it would be wrong. Two things in it tempt a candidate. The first is ‘which’: some style guides prefer ‘that’ for a defining relative clause, but that is a preference and not a rule of grammar, and ‘which’ introducing a defining clause about an inanimate thing is entirely standard, especially in British usage. What would be an error is using ‘who’ for a car or ‘which’ for a person. The second is ‘went past’, which is often marked in error by candidates who have been drilled on the past/passed confusion and reach for it from memory. The drill runs the other way: ‘passed’ is the verb form, ‘past’ is the preposition, adverb or noun, and after ‘went’ only the preposition can stand.
(b)when we were driving on the highway — There is no error here either. The past continuous ‘were driving’ describes a situation already under way when the car overtook, and it is the tense English uses for the background of a narrative. A candidate who suspects this part is usually applying a rule about not mixing tenses in one sentence — but no such rule exists. Mixing a simple past with a past continuous is not an inconsistency; it is how English marks one action as brief and the other as extended. ‘When’ is also correct as the conjunction of time, and ‘while’ would do just as well without making ‘when’ wrong.
(c)must have been doing at least a hundred miles an hour. — This is the part most often suspected, because it is the longest and carries the unfamiliar-looking string ‘must have been doing’, yet it is correct. ‘Must’ is being used to draw a confident inference about the past, which is what the perfect form ‘must have’ expresses, and the continuous ‘been doing’ is right because the inference concerns speed maintained over the moment of overtaking rather than a completed act. Substituting ‘must be doing’ would put the deduction in the present and clash with the past-tense narrative; substituting ‘had to be doing’ would turn a deduction into a requirement. Note also ‘an hour’, which is correct: the article before a word is chosen by the sound the word begins with, and ‘hour’ begins with a vowel sound because its h is silent.

Concept

Three separate points of grammar are being tested at once here, and each is worth holding on to.

FIRST, past and passed. ‘Passed’ is the past tense and past participle of the verb ‘to pass’: he passed the examination, the bus has passed. ‘Past’ is everything else — a preposition (he walked past the gate), an adverb (the years slipped past), an adjective (the past week) and a noun (a thing of the past). The test is simple: if the word is doing the work of the verb, it is ‘passed’; if a verb is already present, as ‘went’ is here, the word that follows is ‘past’.

SECOND, the simple past against the past continuous. English uses the continuous for an action extended in time and the simple past for a shorter action that falls inside it, which is why ‘when we were driving’ sits comfortably beside ‘went past us’. The same pattern appears with ‘while’, and with ‘as’: as I was leaving, the telephone rang.

THIRD, modals of deduction. ‘Must have’ expresses near-certainty about the past on the strength of evidence — she must have left already, the lights are off. Its opposite is ‘cannot have’ — he cannot have seen us, he was facing the other way — and its weaker cousins are ‘may have’, ‘might have’ and ‘could have’, which express possibility. Add the continuous and the deduction becomes one about an action in progress: ‘must have been doing’, ‘must have been waiting’. This family is quite distinct from ‘must’ meaning obligation, which has no perfect form of its own and borrows ‘had to’ for the past.

The item belongs to the ‘Spotting Errors’ block of Part A, which prints a single Directions paragraph over the first item of the set. Those Directions explain the unusual layout: one sentence is divided into three underlined parts labelled (a), (b) and (c), the candidate marks the part that contains an error, and (d) stands for ‘No error’. The transcription reproduces the underlining with vertical bars, because the boundaries matter — a fault belongs to whichever segment contains it.

This sentence is a good example of what the block really tests, which is restraint. It is long, it contains a relative clause, a subordinate time clause and a four-word modal chain, and every one of those is a place where a candidate can talk themselves into finding a fault. The method that works is to take each segment on its own terms and ask a specific question of it — is this the right word class, is this tense doing a job the sentence needs, does this article match the sound that follows — rather than reading the whole sentence for how it feels. A sentence can sound elaborate and still be perfectly built.

On this booklet the item is set over two printed rows, with segments (a) and (b) on the first and (c) with ‘No error’ on the second, each label sitting under its stretch of the sentence.

Key facts

‘Passed’ is the verb form; ‘past’ is the preposition, adverb, adjective or noun. After a verb such as ‘went’, only ‘past’ can follow — ‘went past’, never ‘went passed’.
The past continuous supplies the longer background action and the simple past the shorter event inside it: when we were driving, a car went past.
‘Must have’ + past participle expresses a confident deduction about the past, not an obligation; its negative counterpart is ‘cannot have’, and the weaker forms are ‘may/might/could have’.
‘Must have been’ + -ing makes the deduction about an action that was in progress at that past moment.
‘Must’ meaning obligation has no perfect form; the past of that sense is ‘had to’.
The choice between ‘a’ and ‘an’ follows the SOUND the next word begins with, not its spelling — ‘an hour’ because the h is silent.
‘Which’ is correct for things and ‘who’ for persons; using ‘which’ in a defining clause is standard grammar, whatever a style guide may prefer.
In this block the labels (a), (b) and (c) mark the three underlined parts of the sentence and are simultaneously the answer choices, and (d) is the separate ‘No error’ choice.

Three separate points of grammar — and all three are sound

(a) The car which went past us→‘Past’ is the preposition meaning by or beyond, and it is what follows the verb ‘go’ — go past, drive past, walk past. ‘Passed’ is the verb form, and ‘went passed’ would be two verbs in a row. ‘Which’ is correct for a thing; a style guide’s preference for ‘that’ in a defining clause is a preference, not a rule of grammar.

(b) when we were driving on the highway→The past continuous supplies the longer action already under way and the simple past the shorter event inside it — the phone rang while I was cooking. Mixing the two is not an inconsistency; it is how English sets one action against another.

(c) must have been doing at least a hundred miles an hour→‘Must have’ is a deduction, not an obligation — near-certainty about the past drawn from evidence. The continuous ‘been doing’ is right because the inference is about speed maintained through the moment of overtaking rather than a completed act. ‘An hour’ takes ‘an’ because the h is silent.

(d) No error→Every segment stands, so the separate ‘No error’ choice is the answer. Segment (c) is the part most often suspected, because it is the longest and carries the unfamiliar-looking string ‘must have been doing’.

The modal family of deduction→‘Must have’ is near-certainty about the past. Its negative counterpart is ‘cannot have’ — he cannot have seen us, he was facing the other way. ‘May have’, ‘might have’ and ‘could have’ are the weaker forms. ‘Must’ meaning obligation has no perfect form of its own and borrows ‘had to’ for the past.

past against passed→If the word is doing the work of the verb it is ‘passed’ — he passed the examination, the bus has passed. If a verb is already present, as ‘went’ is here, what follows is ‘past’, which is also adverb, adjective and noun: the years slipped past, the past week, a thing of the past.

Study next

Modals of deduction and their perfect forms: must have, cannot have, may have, might have, could have.Obligation modals against deduction modals — must, have to, had to, ought to, should — and why only the deduction sense takes ‘must have’.Past simple against past continuous, and the conjunctions when, while and as that link them.Confusable word pairs that spotting-errors items are built on: past/passed, lose/loose, affect/effect, principal/principle, stationary/stationery.Relative pronouns who, which and that, and the difference between a defining and a non-defining relative clause.The a/an rule as a rule about sound: an hour, an honest man, a university, a one-rupee note, an MP.

Common traps

Marking ‘went past’ as a past/passed error. The confusion is real, but here the preposition is the correct choice precisely because a verb already stands before it.
Treating a mixture of simple past and past continuous as a tense inconsistency. The two tenses are doing different jobs in the same sentence, which is normal English.
Suspecting ‘must have been doing’ because the chain of auxiliaries looks unwieldy. Length is not an error, and this is the standard form for a deduction about a past action in progress.
Marking the longest segment because it offers the most to read. Segment length has nothing to do with where a fault lies.
Rewriting ‘which’ as ‘that’ on the strength of a style preference and calling the original wrong.

Spotting-errors items on EPFO EO/AO papers stay inside a narrow set of points: subject–verb agreement, articles, prepositions tied to particular verbs, tense sequence, the confusable word pairs, and the misuse of much/many and few/little. Sentences keyed to ‘No error’ are built to look suspicious — a long modal chain, an unusual but correct preposition, a construction that is rarer in speech than in writing. The productive habit is to name the fault before marking a segment: if you cannot say which rule is broken and how the segment should read instead, you have not found an error, you have found something unfamiliar.

Related PYQs

EPFO_EOAO_2020_Q18Open & attempt →

Raju will be back home (a) | in an year (b) | after his stay abroad. (c) | No error (d)

(a) Raju will be back home
(b) in an year
(c) after his stay abroad.
(d) No error

Answer(b) in an year

The companion article item in this block: there the phrase ‘in an year’ is the fault, and reading it beside ‘an hour’ here shows that the a/an choice follows the sound a word starts with, not its spelling.

EPFO_EOAO_2020_Q16Open & attempt →

Directions : Each item in this section has a sentence with three underlined parts labelled (a), (b) and (c). Read each sentence to find out whether there is any error in any underlined part and indicate your response in the Answer Sheet against the corresponding letter i.e., (a) or (b) or (c). If you find no error, your response should be indicated as (d). Neither the servants (a) | nor the clerk (b) | has done this. (c) | No error (d)

(a) Neither the servants
(b) nor the clerk
(c) has done this.
(d) No error

Answer(d) No error

The item that carries the Directions block for this whole set and explains the layout of three labelled segments with ‘No error’ as the fourth choice.

Practice

practice — not a real PYQ
The train had already (a) | past the station (b) | by the time we reached the platform. (c) | No error (d)
- (a)The train had already
- (b)past the station
- (c)by the time we reached the platform.
- (d)No error
Answer(b) past the station — the sentence needs the verb, so it must read ‘passed the station’. With ‘had already’ standing before it, the slot calls for a past participle, and ‘past’ is a preposition and cannot fill it. Part (a) is correct, and part (c) correctly uses the simple past in the time clause against the past perfect of the main clause.
practice — not a real PYQ
She must have been (a) | waiting for us at the gate (b) | for more than a hour. (c) | No error (d)
- (a)She must have been
- (b)waiting for us at the gate
- (c)for more than a hour.
- (d)No error
Answer(c) for more than a hour. — the article must be ‘an’, because ‘hour’ begins with a silent h and so with a vowel sound. Part (a) is a correct deduction about the past, and part (b) correctly continues it with the -ing form for an action that was in progress.

Why