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 creditcard 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? ['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 a credit-card logo than when the tray has no logo.', 'The effect noted in the studies is not limited to patrons who have credit cards.', '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.']