Here's a problem to solve: Sam poured water on a pile of dirt and observed that some dirt eroded from the pile. Which question could he test to learn more about erosion?

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

- A: How long will the dirt stay wet?
 
- B: What types of animals live in the dirt?
 
- C: Will adding more water change the type of dirt?
 
- D: Do different types of dirt wash away at different rates?
 