各位好，我是【經典】謝忠理。
這題除了文字敘述落落長之外，結構其實很容易，答案也沒有爭議。
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 的支持題有 4 種類型：
1. 因果支持題
2. 對照組支持題
3. 反駁的反駁支持題 (取非支持題)
4. 歸納支持題
本題屬於第 2 類。
對照組支持題的答案會以「不同實驗，得不同結果」方式陳述，用以支持原文。
根據我們在國高中做實驗時所學，想要了解某因素是否會影響結果時，我們會將
此因素之外的所有變因控制不變，然後調整這個變因，若結果隨之而變，那就證
明了此因素會影響結果。
我們來看原文所做的實驗與結果：
條件 1. pay bill in cash
條件 2. bill is presented on a tray that bears a credit-card logo
結果：leave larger tips
推論：credit-card logo
-> reminds one his/her spending power
-> larger tips
接著來對照答案 (B)：
條件 1. pay bill in cash (沒寫，但是跟著原文而來)
條件 2. bill is presented on a tray that bears a credit-card logo
條件 3. under financial pressure from their credit-card
obligations
結果：tip less
推論：credit-card logo
-> reminds one his/her financial pressure
-> smaller tip
因此，若以原文為實驗組，那麼答案 (B) 就是構成了對照組：
改變的變因：顧客的財力，高支付力 -> 低支付力
結果隨之而變：支付小費，高小費 -> 低小費
結論：(B) 以對照組支持法提供了 5 個選項中最佳的支持。
若對於其他答案有疑問，可以提出疑問之處，我再進行說明。
【經典美語】謝忠理
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