Choose the correct phrasal verb: The professor asked the student to ___ on her thesis argument.

Correct — B. Meaning decides: a professor who asks about a thesis argument wants more detail on it.

Expand on means say more about something, adding detail and explanation: expand on a point, expand on an argument.

The printed stem already has on after the blank, so the key reads it as 'asked the student to expand on her thesis argument', with one on → option (b).

Why the others are wrong

• (a)
  follow up — Follow up plus the printed on gives 'follow up on her thesis argument', which is grammatical and means pursue it further. It does not ask for more detail, the sense the key reads. See the dispute note.
• (c)
  point out — Point out means draw attention to something, and it takes a direct object: point out a flaw. 'Point out on her thesis argument' is not English, and pointing out adds no detail.
• (d)
  call for — Call for means demand or require: the situation calls for patience. The professor is the one making the request here, and the student is asked to work on her argument, not to demand it.

A phrasal verb is a verb plus a particle (on, up, out, for) that works as one unit of meaning.

Expand on, also expand upon, means give more detail about something already said or written. Elaborate on and enlarge on are close synonyms.

The distractors are real phrasal verbs with other senses: follow up on means pursue further, point out means draw attention to, call for means demand.

Key facts

• Expand on (or expand upon): give more detail about something.
• Elaborate on and enlarge on are close synonyms of expand on.
• Follow up on: pursue something further or take further action on it.
• Point out: draw attention to something. It takes a direct object.

Common traps

• Choosing follow up because follow up on is a real phrasal verb, without checking whether it gives the sense of adding detail
• Reading point out as 'explain', when it only means draw attention to

No directly related past PYQ was found.