这个题给的答案是B我为什么应该选A呢？

mike125615212 · 发表于 2012-3-22 18:30:47

30. GWD17-Q30:
In a study conducted in Pennsylvania, servers invarious restaurants wrote “Thank you” on randomly selected bills beforepresenting the bills to their customers. Tips on these bills were an average of three percentage points higherthan tips on bills without the message. Therefore, if servers in Pennsylvaniaregularly wrote “Thank you” on restaurant bills, their average income from tipswould be significantly higher than it otherwise would have been.

Which of the following is anassumption on which the argument relies?

A. The “Thank you” messages would have the sameimpact on regular patrons of a restaurant as they would on occasional patronsof the same restaurant.
B. ！Regularly seeing “Thank you” writtenon their bills would not lead restaurant patrons to revert to their earliertipping habits.
C. The written “Thank you” reminds restaurantpatrons that tips constitute a significant part of the income of many foodservers.
D. The rate at which people tip food servers inPennsylvaniadoes not vary with how expensive a restaurant is.
E. Virtually all patrons of the Pennsylvania restaurantsin the study who were given a bill with “Thank you” written on it left a largertip than they otherwise would have.

sdcar2010 · 发表于 2012-3-22 20:46:11

A) is one possibility to explain the phenomena, but A) is not necessary for ALL phenomena.

B) on the other hand is necessary for ALL cases.

Necessary assumption. Use negation. If you negate B), the argument falls apart. Thus, B) is necessary.

这个题给的答案是B我为什么应该选A呢？

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