Write only three answer, . . . . . . ?

Answer: Option C

The correct sentence is: "Write only three answers, will you?"

In question tags, when the main clause is an imperative (command/request), the tag is usually "will you" for a neutral or polite request.

Option B: "won’t you" is sometimes used for persuasion or encouragement, but it is less common in direct instructions.

Other options like "don’t you" and "do you" are incorrect in this context.

Thus, the best choice is Option C: will you.