Change the following sentences into Active Voice by choosing the most…

The correct answer is Option (3) → Who taught you French?

Passive question with "By whom" into the active voice:

Change	Passive	Active	Why
Agent (by ...) becomes subject	By whom	Who	“By whom” asks about the doer, so in the active voice it becomes Who, the subject.
Tense kept	were ... taught	taught	“Were ... taught” is simple past passive, so the active verb is the simple past taught. No “did” is needed because “Who” is the subject.
Subject becomes object	you (subject)	you (object)	The passive subject you becomes the object.
Full sentence	By whom were you taught French?	Who taught you French?

"French" stays as it is.

Example: By whom was this letter written? → Who wrote this letter?

Why the Other Options are Incorrect?

Option 1: By whom did you teach French? — Incorrect.

• It makes "you" the teacher, which reverses the meaning.
• "By whom" does not belong in an active question.

Option 2: Who teaches you French? — Incorrect. The tense changes from the past "were taught" to the present "teaches".

Option 4: By who taught your French? — Incorrect. It is ungrammatical: "By who" has no place in the active voice, and "your French" changes the object.