I was really impressed with the intro. Nice quality graphics wise and a decent level of detail. It would be nice if you could skip it as you have to sit through it each time during replay.
+ The quiz is certainly educational.
+The inbetween-levels animation was also rewarding. Though, It would be nice if there was more of a reward to get to the next page. Perhaps you could make a basic counter system to grade accuracy or even longest chain of correct answers. This would really help connecting the questions as a single solid game.
+The buttons worked properly, were made well, and had a nice theme. It would be nice if the zone behind the text was also part of the button.
+The pictures were also used appropriately and didn't take away from the animation as a whole, which is hard to do with linear fills. I suggest you also try adding something more to the background during the test than just the linear fills as they came off as a bit drab.
This is still a respectable quiz. Really nice work on the intro--if you made that into a preloader--it'd make this animation spectacular.