各位好，我是【经典】谢忠理。
这题除了文字叙述落落长之外，结构其实很容易，答案也没有争议。
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?
(A) The effect noted in the studies is not limited to patrons who have
credit cards.
(B) 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.
(C) In virtually all of the cases in the studies, the patrons who paid
bills in cash did not possess credit cards.
(D) In general, restaurant patrons who pay their bills in cash leave
larger tips than do those who pay by credit card.
(E) 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.
GMAT 的支持题有 4 种类型：
1. 因果支持题
2. 对照组支持题
3. 反驳的反驳支持题 (取非支持题)
4. 归纳支持题
本题属于第 2 类。
对照组支持题的答案会以“不同实验，得不同结果”方式陈述，用以支持原文。
根据我们在国高中做实验时所学，想要了解某因素是否会影响结果时，我们会将
此因素之外的所有变因控制不变，然后调整这个变因，若结果随之而变，那就证
明了此因素会影响结果。
我们来看原文所做的实验与结果：
条件 1. pay bill in cash
条件 2. bill is presented on a tray that bears a credit-card logo
结果：leave larger tips
推论：credit-card logo
-> reminds one his/her spending power
-> larger tips
接着来对照答案 (B)：
条件 1. pay bill in cash (没写，但是跟着原文而来)
条件 2. bill is presented on a tray that bears a credit-card logo
条件 3. under financial pressure from their credit-card
obligations
结果：tip less
推论：credit-card logo
-> reminds one his/her financial pressure
-> smaller tip
因此，若以原文为实验组，那么答案 (B) 就是构成了对照组：
改变的变因：顾客的财力，高支付力 -> 低支付力
结果随之而变：支付小费，高小费 -> 低小费
结论：(B) 以对照组支持法提供了 5 个选项中最佳的支持。
若对于其他答案有疑问，可以提出疑问之处，我再进行说明。
【经典美语】谢忠理
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