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?

The effect noted in the studies is not limited to patrons who have credit cards. 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. In virtually all of the cases in the studies, the patrons who paid bills in cash did not possess credit cards. In general, restaurant patrons who pay their bills in cash leave larger tips than do those who pay by credit card. 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.

为什么答案是B啊？（我选择的是E）

心理学家的观点是：当消费者看到credit card 的logo时，认为使用credit card 时的消费能力要比使用cash强，所以他们愿意多付小费。

可是答案B的意思是：当消费者看到logo时候，感到了经济压力，所以付的消费比没看到logo的时候少。（这不是和本文观点矛盾吗？）

这是一个因果结构的加强题，思路是，没有假设的原因，就没有题中描述的现象出现。

这道题中的应用是：到看到logo，感到经济压力（没有假设的原因），少付钱（没有题中描述的现象）