Is there only one answer to a question?

Answer 1

A question may be either an expression used to make a request for information, or else the request itself made by such an expression. Not all questions have answers . While some questions have concrete, verifiable answers. (e.g: Is the sun hot?), some do not. eg) Did Julius ceaser like his eggs scrambled, boiled or sunny-side up? Any answer to this question, would not be an answer per se, but an assumed, unverifiable answer, meaning it is not an answer at all but just an opinion being voiced, therefore the question asked, although answered, is not answered. So conclusively, any answer given to said question will not answer the question therefore the question will remain un-answerable although answers might be given. so to answer your question, Opinions can and always will be given to any question asked, however, they might not always qualify as answers.

Answer 2

When asking a rhetoric question; Yes. When answering a genuine question with various answers of which you can provide arguments; No.

Don't forgot to take into account that "Yes/No" questions are opinionated and does require one to take a stance thus you'd get varied answers proving that some times there can be more than one answer to a question.

Answer 3

Yes, an answer can have an answer which is a question, especially if you are playing "Jeopardy!"