【求教】关于餐厅小费的那道题

Lilchal

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?

A-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.
B-bRegularly seeing “Thank you” written on their bills would not lead restaurant patrons to revert to their earlier tipping habits.
C-The written “Thank you” reminds restaurant patrons that tips constitute a significant part of the income of many food servers.
D-The rate at which people tip food servers in Pennsylvania does not vary with how expensive a restaurant is.
E-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.


知道B为什么正确
但队E选项还有疑惑

我对E选项的理解

是不是因为题中明确写了这个study的结果 所以这个study天然是成立的
E就无法取非去验证呢？？

因为做题是我取非E 如果study中的patron没有给很多小费 那么study的结论不成立
也就谈不上说regularly wrote thank you in bills。。也就没有average income from tips higher了...

而且这题是不是study本身不在“因”里面啊

Lilchal

没有人吗TAT

VincentFSJ

E是所有的patron都tip higher than they would otherwise；
第一句话是背景，对背景假设有什么用呢？