Under which of the following conditions would a fossil most likely form?

Under which of the following conditions would a fossil most likely form?

A. a living thing dies and sediment is very slowly deposited on top of its body.
B. a living thing dies and sediment quickly covers its body.
C. a living thing dies and its skeleton is left exposed to the elements.
D. a living thing dies and radioactive element breaks down its body.

Answer : 

A) a living thing dies and sediment is very slowly deposited on top of its body.