Answer + object
Incorrect : Answer to any five of the following questions.
Correct: Answer any five of the following questions.
Note: When the word "answer' is used as a noun, it takes the preposition "to" after it. For example:
Your answer to this question is wrong.
But "reply" and "respond" as verbs are followed by "to". You should say:
You must reply/respond to my questions.
