Here's a problem to solve: Which BEST describes the surface of the Earth over billions of years?

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

- A: A flat surface is gradually pushed up into higher and higher mountains until the Earth is covered with mountains.
 
- B: High mountains gradually wear down until most of the Earth is at sea level.
 
- C: High mountains gradually wear down as new mountains are continuously being formed, over and over again.
 
- D: High mountains and flat plains stay side by side for billions of years with little change.
 