Here's a problem to solve: Which is the best evidence that rocks found deep underground were once exposed at the surface?

Among the 4 following options, which is the correct answer?

- A: The rocks have been melted by a magma.
 
- B: The rocks have been broken by faults.
 
- C: The rocks have been weathered by water.
 
- D: The rocks have been folded by pressure.
 