I have an interview with a professor for a Ph.D. position in the US next week. As I was going through the possible questions that a professor can ask, so I was wondering what if they ask me if I have any questions regarding working in that specific lab? I mean yes I can ask some basic questions (which may be irrelevant too). As there are so many people from academia, what you usually expect a candidate to ask? What can be a reasonable and valid question?