Choose the appropriate Active Voice of given sentence. By whom were y…

The correct answer is Option (2) → Who taught you French?

Passive question with "By whom" to 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 the subject Who.
Tense kept	were taught	taught	When “who” is the subject of a question, no helping verb “did” is used. The verb takes the tense of the passive: “were taught” is simple past, so taught.
Subject becomes object	you (subject)	you (object)	“You” goes back to the object position: taught you.
Full sentence	By whom were you taught French?	Who taught you French?

The second object "French" stays as it is.

Example: By whom was this song sung? → Who sang this song?

Why the Other Options are Incorrect?

Option 1: Who did teach you French? — Incorrect. When "who" is the subject, "did" is not used in a plain question. "Did teach" is used only for special emphasis.

Option 3: Who do teach you French? — Incorrect. "do" is present tense and does not agree with "who" (which takes a singular verb). The original is in the past.

Option 4: Who was teach you French? — Incorrect. "was teach" is not a verb form. "Was" cannot be followed by the base form "teach".