Diamonds are made

Question

1. at the surface of earth
2. magma moving at supersonic speeds deep inside the earth
3. in river beads
4. in limestone caverns

Answer 1

2 is the best answer, and it is not entirely correct, but the other answers are worse.

Answer 2

I don't know that I like any of the answers. Here is a site to read about how diamonds are formed. http://en.wikipedia.org/wiki/Diamond

Answer 3

2. magma moving at supersonic speeds deep inside the earth