The teacher told the student to abridge the essay he had written.

Answer: Option A

Abridge : shorten (a piece of writing) without losing the sense.
Amplify : enlarge upon or add detail to (a story or statement).
Shorten : make or become shorter.
Increase : become or make greater in size, amount, or degree.
Modify : make partial or minor changes to (something).

Antonym of Abridge is Amplify