> Does anyone know if, when a contestant "asks the audience" every person in the audience is obliged to press the buzzer?
Don't know for sure but I think they are, yes. They may also be prompted have a wild guess and not just press, say, "A" if they don't know. The reason I think this is that one some of the tougher questions, the distribution seems quite evenly spread. I have never yet seen a question where one answer got more than 25% and the other three got less than 25% and the answer with more was wrong. Things get very tricky when more than one answer gets more than 25%, though.