Select the option that expresses the following sentence in active voice.
By whom were you taught English grammar and composition?

Correct option is D

The correct active voice for the given sentence is (d) "Who taught you English grammar and composition?"
Active Voice: In Active voice the subject is the one doing the action.
Passive Voice: In Passive voice the subject is the recipient of the action.
To convert active voice into passive voice the object becomes the subject and the subject becomes the object.
For Simple Past Tense as given in the question the structure for changing a sentence from active to passive and vice versa is:
(Active voice) Who + V2 + subject + base form of the verb + object?
(Passive voice) By Wh-word + was/were + object + past participle of the verb + subject?