Change the following from active to passive: The professor could have been explaining differential topology for hours.
- (a)Differential topology could have be being explained for hours by the professor.
- (b)Differential topology could have explained for hours by the professor.
- (c)Differential topology could have been being explained for hours by the professor.
- (d)Differential topology could have had been been explained for hours by the professor.
Answer
Why
Correct — C. The active verb is could have been explaining: modal could, perfect have been, and the continuous -ing.
In the passive, the -ing passes to being and the main verb becomes its past participle:
been explaining → been being explained
The object differential topology becomes the subject, and the professor moves into the by-phrase. That is option (c).
Why the others are wrong
- (a)Differential topology could have be being explained for hours by the professor. — have be being is ungrammatical. The perfect auxiliary have must be followed by a past participle, so be has to be been.
- (b)Differential topology could have explained for hours by the professor. — could have explained contains no form of be, so it is active, not passive. With differential topology as subject, it says the subject did the explaining.
- (d)Differential topology could have had been been explained for hours by the professor. — have had been been repeats the perfect and repeats been, and drops being. It is not an English verb form, and the continuous sense of for hours is lost.
Concept
Passive = be + past participle, added to the end of the existing auxiliary chain. Keep every auxiliary of the active verb. The new be takes whatever form the auxiliary before it requires.
After a continuous be, it takes -ing: is explaining → is being explained
After a perfect have, it becomes been: has explained → has been explained
Here the passive be follows the continuous been, so it is being.
Been being sounds heavy, but it is the regular passive of a perfect continuous verb. Each rejected option is either ungrammatical or active, so the awkwardness is no reason to doubt the key.
Key facts
- Passive of a perfect continuous verb: have, has or had been + being + past participle.
- Passive of a modal perfect: could have been + past participle, as in could have been explained.
- Auxiliaries keep a fixed order: modal, perfect have, continuous be, passive be, then the main verb.
Study next
Common traps
- Writing have be after a perfect auxiliary, where have always needs the past participle been.
- Dropping being, and with it the continuous sense that for hours signals.
Perfect continuous verbs turned passive also decide 14 Sep 2025, 09:00, English Q.12, where had been debating becomes had been being debated and the decoys are the same had be being and had had been been.
12 Sep 2025, 09:00, English Q.12 turns have been neglecting into has been being neglected.
Related PYQs
No directly related past PYQ was found.