This question is about converting an active voice sentence into passive voice. The original sentence is: "Who taught her French?"

Step 1: Identify the Voice
The given sentence is in the active voice. In active voice, the subject performs the action. Here, "Who" is the subject performing the action "taught".

Step 2: Understand Passive Voice Construction
To convert a sentence to passive voice:

• The object of the active sentence becomes the subject of the passive sentence.
• The verb changes to a form of "be" + past participle.
• The original subject is introduced with "by" (becoming the "agent").

For a question starting with "Who", the passive form typically starts with "By whom".

Step 3: Analyze the Given Sentence
Let's break down the active sentence: "Who taught her French?"

• Subject: Who
• Verb: taught (past tense of teach)
• Indirect Object: her
• Direct Object: French

In the passive voice, the direct object ("French") or the indirect object ("her") can become the subject. The more common construction is to make the indirect object the subject: "She was taught French by whom?" However, to form a proper question, we rearrange it to start with the question word: "By whom was she taught French?"

Step 4: Evaluate the Options
Let's examine each option:

• Option 1: "Whom has taught French to her?" - This is incorrect. It is still in active voice ("has taught") and uses the wrong question word order for a passive construction.
• Option 2: "Who is teaching her French?" - This is incorrect. It is in active voice (present continuous tense) and does not convert to passive.
• Option 3: "By whom was she taught French?" - This is correct. It follows all the rules of passive voice: the indirect object "her" becomes the subject "she", the verb is changed to "was taught" (past tense of 'be' + past participle of 'teach'), and the original subject is introduced with "by" ("by whom").
• Option 4: "Who is that who teach her French?" - This is incorrect and grammatically awkward. It is not a passive construction.

Final Answer: The most appropriate passive form is "By whom was she taught French?"

Related Topic: Active and Passive Voice

Voice is a form of verb showing whether the subject performs an action (active voice) or receives the action (passive voice). The passive voice is used when the focus is on the action or the object of the action, not on who performed it. The structure is: Subject + form of 'be' + Past Participle + by + agent.

Important Formula

The general formula for converting a simple past tense active sentence to passive is:
Active: [Subject] + [V2] + [Object]
Passive: [Object] + was/were + [V3] + by + [Subject]