Take a look at this Critical Reasoning question from 1000 CR:

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.

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This one is interesting since we are not provided with a conclusion, so we have to draw one based on the evidence.

Evidence: Bottom of middle layer contains pottery 3. Pottery 3 is made AFTER the destruction.

I’m going to draw a picture, because drawing is fun, and totally under-rated when it comes to GMAT Critical Reasoning. 🙂

We can infer that usually the deeper the level = the older the time period. Since as we move forward in time, we generally build up on things.

So, the city was probably destroyed around the lower layer, or in the middle layer but beneath where the pottery was found.

Question: What casts doubt on the Type 3 pottery in the middle layer/destruction of city inference?

Prediction: If the pottery was moved around — if the location doesn’t represent the time period accurately.

A – decent choice, shows pottery could’ve been moved
B – doesn’t comment on Type 3 pottery
C – this implies at some point the middle-layer people used the wall below them to build up — but doesn’t show that the pottery could have moved down or up
D – Fire is totally irrelevant
E – “at the time of the siege” is vague — and this doesn’t relate at all to the pottery evidence

The correct answer is (A).