I'll go with C.
It cant be A because:
The passage states that the middle layer contains pieces of pottery of type 3 , but the lower layer does not contain the same pieces. Just because the lower layer does not have the same type of pieces does not mean that the lower layer contains remains of the destroyed city.
The bottom of the middle layer contains some pieces of pottery of type 3, known to be from a later period than the time of the destruction of the city, but the lower layer does not
Now, the remains of the destroyed city cannot be in the lower-lower level or sub lower levels... so where will it go....