Here's a problem to solve: For many years, scientists have found fossils in rock layers in all parts of the world. Eventually scientists discovered that many of the rock layers showed the same pattern of older fossils being located in deeper rock layers and younger fossils being located in shallower layers. This discovery is an example of how scientific knowledge changes as

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

- A: fossils are preserved in different ways.
 
- B: conclusions about fossils are revised into questions.
 
- C: fossils are formed in different areas.
 
- D: new fossil evidence is reviewed.
 