A) The effect noted in the studies is not limited to patrons who have credit cards.
- We're told in the passage that credit card holders are willing to spend more. Not limiting the study to patron who have credit cards is quite irrelevant to supporting the conclusion.
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.
- not important
D) In general, restaurant patrons who pay their bills in cash leave larger tips than do those who pay by credit card.
- If so, nothing to do with the credit card logo
E) The percentage of restaurant bills paid with given brand of credit card increases when that credit cardâ€™s logo is displayed on the tray with which the bill is prepared.
- does not support the theory
I'll take B. We're told the hypothesis is seeing a credit-card logo makes many credit-card holders willing to spend more because their spending power > immediate cash. So if patrons are under financial pressure form credit-card obligations, they will tip a little less, although it's sitll more compared to a tray with no logo.