GWD-17-Q30
In a study conducted in Pennsylvania, servers in various restaurants wrote “Thank you” on randomly selected bills before presenting the bills to their customers.
Tips on these bills were an average of three percentage points higher than tips on bills without the message.
Therefore, if servers in Pennsylvania regularly wrote “Thank you” on restaurant bills, their average income from tips would be significantly higher than it otherwise would have been.
Which of the following is an assumption on which the argument relies?
The “Thank you” messages would have the same impact on regular patrons of a restaurant as they would on occasional patrons of the same restaurant. Regularly seeing “Thank you” written on their bills would not lead restaurant patrons to revert to their earlier tipping habits. The written “Thank you” reminds restaurant patrons that tips constitute a significant part of the income of many food servers. The rate at which people tip food servers in Pennsylvania does not vary with how expensive a restaurant is. - Virtually all patrons of the Pennsylvania restaurants in the study who were given a bill with “Thank you” written on it left a larger tip than they otherwise would have.
答案是B。但是B中说的顾客暗指"regular patron"。但是B对于"occational patron"根本就不起任何作用。那么在所有的"patron"中，是"regular patron"占多数，还是"occasional patron"？不知道！！！所以B充其量可以strengthen结论，但是还不够格作为assumption。
再来看E：
E说“收到thank you bill的顾客最后给的小费比他们起初打算给的要多”。多么漂亮的比较啊！！如果对E取非，就变成了“不管bill上写不写thank you，顾客给的小费都是一样多”。既然是这样，那还写"thank you"干什么？反正小费都是一样一样一样的！
E不成立，结论必不成立！ | 
