Hardest school subect you''ve ever studied?

Algebra, by far. I've only managed to pull a B- in that class while all of my other classes were high B's and A's. The concepts were hard to grasp, even with extra help and no amount of explainations could save me.

Chemistry is a close second though. The teacher gave us 50 questions to do in the book like every 2 nights. Repetitive calculation crap, too -.-