What 3 choices do you have in responding to illegal interview questions?

Depending on what country and sometimes State/Province you're in there are questions that are legal, or illegal and they can differ. So its important to know what you're rights are depending on where you're applying a job.

some answers could be:

I've not been asked that question before, can you tell me how that relates to the position/job?

I'm not sure what you're concerns are related to this question, could you give me more information

or you could just say you're uncomfortable with this question.

See some ideas on a site called Careego - innapropriate questions to get some more ideas