Here's a problem to solve: Coal is solid rock that began as organic material that was deposited in a swamp. The formation of coal suggests that

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

- A: coal is made mostly of skeletal remains of animals.
 
- B: coal is formed from magma that has solidified over time.
 
- C: it quickly becomes petrified when water is removed.
 
- D: geologic processes continue over millions of years.
 