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.现象：有信用卡标志的托盘会收到更多小费
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.
增强解释可信度的选项,
解释是否合理的关键在于people who are not reminded of their own excess purchasing power paid more tips,也就是顾客是否看到标志就被提醒到他们的信用卡
B选项证明了这一点
而A消弱了,证明很多顾客没有被提醒到有信用卡这回事就付了更多小费
C也是和A一样
D也是削弱,用信用卡的人已经意识到自己可以花超额但是付的小费较少
E具体到某一品牌的信用卡,而题目给的解释是顾客通过信用卡标志意识到自己有信用卡才花更多,不能由具体的某品牌信用卡的现象推一个更加大,抽象的结论.