help for the budding scientist

Earlier this week I received the following email from a future paleontologist, Adrienne:

Hey, Andie, I have to do a science fair experiment... the kind where you have to answer a question like, "What different fruits and veggies have more vitamin C?" (That's an example, I did it in 5th grade (2nd place!))
Anyway, I have been searching the interweb and have been so far coming up blank. I was wondering if you guys had any ideas, anything that you remember possibly doing?

We never had science fairs at my school, so I have no suggestions for young Adrienne. But you, dear readers -- any ideas? If so, please comment away