I think it really is just luck because I'd have to agree with BongoBetty, based on the only time I've been to this attraction.
The questions aren't terribly impossible - that is, they're not terribly impossible if you are at all familiar with the subject. When we were there in March, the questions were definitely "Americanized". Again, not IMPOSSIBLE, but hard for anyone who hasn't had, say, 4th grade Social Studies in the US. In fact, the day we were there, two Canadians were in the Hot Seat (separate times) and both got stumped on US government related questions. The first contestant even used the "Phone a Complete Stranger" lifeline, and, in comedy of ALL comedies, ended up with ANOTHER CANADIAN!! lol It was really very amusing.
I do imagine, however, that the questions and subject matter are rotated so much that it's really just luck of the draw as to what you have to answer. Good luck!!