Why is the archaeological site of pompeii so important to our understanding of roman life now?

If the choices are:

A.   The Romans purposely left Pompeii intact as a monument to the people who died there.

B.   The remains at Pompeii were preserved intact when the volcanic ash covering them hardened, giving a realistic picture and understanding of life there.

C.   Archaeologists and historians from all over the world have sifted through the remains of the city ever since Pliny's account was found during the first century A.D.

D.   Pompeii is the only place where Roman structures can still be seen today.

The answer is:  B ***