[求助]求教一道GWD逻辑题

30. GWD17-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?

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.        Regularly 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.

请问答案为什么选B

把选项B, 取非， 就成了Regularly seeing “Thank you” written on their bills would （not） lead restaurant patrons to revert to their earlier tipping habits.

成了削弱！

原文是说客人对写“thank you" 的帐单，会多付小费。

假设是说客人不会因为习以为常的看到“thank you" 的帐单，而回复到以前的付小费习惯。