This question tests your understanding of verb patterns after the verb "make". The verb "make" is a causative verb, which means it indicates that someone causes something to happen. When "make" is used in the active voice, it is followed by a bare infinitive (the base form of the verb without "to").

The structure is: Subject + make + object + bare infinitive

Let's apply this rule to the sentence: "What made you _____ it ?"

Here, "you" is the object, and the blank requires the verb "do". According to the rule, the correct form is the bare infinitive "do".

Therefore, the correct sentence is: What made you do it?

Why the other options are incorrect:

• to do: Incorrect. "Make" is not followed by a "to-infinitive" in the active voice.
• done: Incorrect. This is the past participle and is not used after "make" in this context.
• doing: Incorrect. "Make" is not followed by a gerund (-ing form).

Related Topic: Causative Verbs

Causative verbs (like make, let, help, have, get) show that the subject is not the doer of the action but is instead causing someone else to do it. Each has its own pattern:

• make + object + bare infinitive (forces someone to do something)
• let + object + bare infinitive (allows someone to do something)
• have + object + bare infinitive (gives someone the responsibility to do something)
• get + object + to-infinitive (persuades someone to do something)

Important Formula

The formula for the verb "make" in the active voice is:

Example: The news made her cry.

Note: In the passive voice ("She was made to cry"), "make" is followed by a "to-infinitive".