请大家解答 GWD 23-Q32

vanchaser

Excavations of the Roman city of Sepphoris have uncovered numerous detailed mosaics depicting several readily identifiable animal species:  a hare, a partridge, and various Mediterranean fish.  Oddly, most of the species represented did not live in the Sepphoris region when these mosaics were created.  Since identical motifs appear in mosaics found in other Roman cities, however, the mosaics of Sepphoris were very likely created by traveling artisans from some other part of the Roman Empire.
Which of the following is an assumption on which the argument depends?
A. The Sepphoris mosaics are not composed exclusively of types of stones found naturally in the Sepphoris area.
B. There is no single region to which all the species depicted in the Sepphoris mosaics are native.
C. No motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city.
D. All of the animal figures in the Sepphoris mosaics are readily identifiable as representations of known species.
E. There was not a common repertory of mosaic designs with which artisans who lived in various parts of the Roman Empire were familiar.

答案是E  为什么不能是C呢
如果motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city. 那就有可能不是other roman city 来的呀。
E 选项我也懂 也对。 但是C为什么不对呢？

sdcar2010

Necessary assumption. Use negation.

If you negate C), you have:
SOME motifs appear in the Sepphoris mosaics that do not also appear in the mosaics of some other Roman city.

If so, it only shows that it is unlikely that artist from S travels to other Roman cities. But it does not say anything about artists coming from other Roman cities to S. So the main conclusion of the argument still holds. Some means 1 or 100 out of 100. If some = 1, there is almost no harm done to the main conlcusion. If some = 100, then we will have a problem. This just proves that C is not necessary for the argument to hold.

vanchaser

Thanks a lot.
I am wondering how i can know to use what skills to solve corresponding questions. Could you tell me?  Or any reference materials I need to read?

sdcar2010

Search for Necessary Assumption and you will find a lot of relevant links.

Or just wait for ten more days and read my post on the subject of the same.