Descartes' answer: "I know God is benevolent, because when I conceive of God, I conceive of benevolence, and God gave me my conceptions. A benevolent God wouldn't lead me astray. Thus, the things I learn through my senses and understand through my reason are right, because a benevolent God wouldn't have it any other way."
4/
I've hated this answer since my freshman philosophy class, and even though the TA rejected my paper explaining why it was bullshit, I *still* think it's bullshit. I mean, I'm a science fiction writer, so I can handily conceive of a wicked God whose evil plan starts with *making you think He is benevolent* and then systematically misleading you in your senses and reasoning, tormenting you for His own sadistic pleasure.
5/