请教 GWD 3-9, 哪位NN能给个指点

下面是GWD 3-9的一道题，看了很多遍都不知道为什么会选B，请哪位高人给个解释，谢谢！

GWD3-Q9:

Studies in restaurants show that the tips left by customers who pay their bill in cash tend to be larger when the bill is presented on a tray that bears a credit-card logo.  Consumer psychologists hypothesize that simply seeing a credit-card logo makes many credit-card holders willing to spend more because it reminds them that their spending power exceeds the cash they have immediately available.

Which of the following, if true, most strongly supports the psychologists’ interpretation of the studies?

1. The effect noted in the studies is not limited to patrons who have credit cards. OK
2. Patrons who are under financial pressure from their credit-card obligations tend to tip less when presented with a restaurant bill on a tray with credit-card logo than when the tray has no logo.

3. In virtually all of the cases in the studies, the patrons who paid bills in cash did not possess credit cards.
4. In general, restaurant patrons who pay their bills in cash leave larger tips than do those who pay by credit card.
5. The percentage of restaurant bills paid with given brand of credit card increases when that credit card’s logo is displayed on the tray with which the bill is prepared.

 答案：B

从答案看，好像应该是减弱而不是加强啊。

题目中的持有信用卡的人用现金消费的时候，看见了信用卡的标志，会觉得自己的消费能力比他们持有的现金要高得多，所以会多给小费，那么，这也是信用卡引起的。

B的意思是说，那些遭受信用卡还贷压力的人看见信用卡标志的时候会给比较少的小费，证明了小费的多少与信用卡有关。所以是加强。