请教一道题目 XDF old book

Question 19-20 are based on the following

Archaeologists seeking the location of a legendary siege and destruction of a city are excavating

In several possible place, 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 form a later period than the time of the destruction of the city, but the lower layer does not.

19.Which of the following hypothesis is best support by the evidence above?

A.      The lower layer contains the remains of the city where the siege took place.

B.      The legend confuses stories from two different historical periods.

C.      The middle layer does not represent the period of the siege

D.      The siege lasted for a long time before the city was destroyed

E.       The pottery of type 3 was imported to the city by traders

20.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 burrow 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 incorporate 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 habitation by fire

E.       Bronze axheads of a type used at the time of the siege were found in the lower level of

Excavation

答案分别为C和A    想了半天不明白 请大家指教 谢谢：）

第一题，  （废墟一般都是按时间一层一层埋上去的）如果中部低层的东西 还没有包含到围攻时期的废墟， 那么中层都不会有， 很可能在底层

第二题， 出的有些主观， 需要联想的太多了，   说那个事实能削弱文中EVIDENCE的说服力，  如果A 选项说 东西都是掉进动物的洞里 而存在的， 那就不能在 ‘层层埋’ 推理中起作用

好像有些明白了 非常感谢！