大全一道题不同的问题，求解

大宝店小二

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 ax heads of a type used at the time of the siege were found in the lower level of excavation.
大家都说A中是因为有G的存在导致不同层中的东西混淆了。我还是不太理解，原谅我弱爆了啊。A的意思不应该是说中层的会掉到下层去吗？但是原文中说反正下层中都没有发现type3啊，即使有G存在下层都没有发现，怎么会削弱结论呢？
求解啊！

大宝店小二

难道是说中层的东西有可能是上层掉落的吗？我凌乱了，继续求解啊！