Need explanation

Yusufulbright wrote:Archaeologists seeking the location of a legendary siege and destruction of a city are excavating in several possible places, including a middle and a lower layer of a large mound. 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.

The force of the evidence cited above is most seriously weakened if which of the following is true?
(A) Gerbils, small animals long native to the area, dig large burrows into which objects can fall when the burrows collapse.
(B) Pottery of types 1 and 2, found in the lower level, was used in the cities from which, according to the legend, the besieging forces came.
(C) Several pieces of stone from a lower-layer wall have been found incorporated into the remains of a building in the middle layer.
(D) Both the middle and the lower layer show evidence of large-scale destruction of habitations by fire.
(E) Bronze axheads of a type used at the time of the siege were found in the lower level of excavation

I answered it wrong. The correct answer seems not related to stimilu.. which confuses me..

First, always post the official answer. It helps people "reverse engineer" an approach and be able to explain how the solution was reached.

My answer is (A), because all the other answers strengthen, or do nothing.

The conclusion is that the lower layer is promising because the layer above it has pottery from a later time period. However, (A) opens up the possibility that objects could appear artificially low in the ground because of collapsing gerbil holes.

(B) STRENGTHENS because this places the enemy forces at that location around that time, strengthening the idea that they sieged and destroyed what had been there.

(C) STRENGTHENS because people building things would use the resources around them. If a city had been destroyed, then people rebuilding would very likely use the materials left over to rebuild. Therefore, while this doesn't point to a siege specifically, it does appear that the city that was around during the lower layer was destroyed at some point before the middle layer, supporting the conclusion.

(D) STRENGTHENS because this supports the notion that the city there was sieged/destroyed during these two time periods.

(E) NEUTRAL - it may strengthen, but just because axheads from that time period were found in that layer, doesn't mean a siege occurred. However, it certainly doesn't weaken/contradict the conclusion.

Thanks for your reply and explanation.. The QA is A..