The first one is from a philosophy class I took:
What do we know? or Can we know anything?
Descartes started with this question. He decided that he wasn't going to assume anything about the world, and see what he could come up with. The first thing he thought of was "I exist" or "I think, therefore I am." (Look at that, something famous on this silly page). Then he tried to figure out something else he could know. He decided he couldn't trust his senses, because sometimes they deceived him. So why couldn't there be this big, evil being whose sole purpose was to deceive him? That means he couldn't trust his sense at all. So he was stuck.
Descartes got out of the pickle by saying that God existed, and because he existed he must be good, and because he was good, he wouldn't deceive poor Descartes. Well, you can see that this is sort of a problem, because why does God have to exist, if all the evidence you have is that you exist? And why does God have to be good? Why couldn't God be the evil deceiver? Descartes didn't have a problem with these questions because of his religious beliefs, but I do. Do you?