I am taking the same Campbell tests, and they are indeed challenging. I have 135% in AP Calc right now (result of a curve that makes the average score 80%; rediculous, I know
), 100% in AP Chem, 98%+ in everything else (including three other weighted classes), and 92% in Bio; this is despite the fact that I'm spending by far the most time for Biology (twice as much, easily, as any for any other class).
Most of the questions seem to come from the diagrams in the textbook. Studying these has helped me quite a bit: I examined the chapters with extreme attention for our recent test on Cellular Respiration, Photosynthesis, Cell Communication, and Mitosis/Meiosis, and it helped. (Got all the questions right.) But it was a ton of information.