How should I handle illegal & inappropriate questions during a construction interview?

Unfortunately employers will ask illegal questions because most may not know what is considered legal or illegal. However if you are asked an illegal or inappropriate question, you should respond letting them know you don't see how this question is relative or appropriate. However sometimes an innocent question should be given an innocent answer- but by law you don't have to answer any such questions- How old you are? Are you single? What country are you from? Do you have children?