答案是D 请帮忙介绍一下其中的关系！

斯巴达

Bank depositors in the United States are all financially protected against bank failure because the government insures all individuals' bank deposits.  An economist argues that this insurance is partly responsible for the high rate of bank failures, since it removes from depositors any financial incentive to find out whether the bank that holds their money is secure against failure.  If depositors were more selective, then banks would need to be secure in order to compete for depositors' money.

The economist's argument makes which of the following assumptions?

(A) Bank failures are caused when big borrowers default on loan repayments.
(B) A significant proportion of depositors maintain accounts at several different banks.
(C) The more a depositor has to deposit, the more careful he or she tends to be in selecting a bank.
(D) The difference in the interest rates paid to depositors by different banks is not a significant factor in bank failures.
(E) Potential depositors are able to determine which banks are secure against failure.

flames001

粗略读下来，题目告诉这样一个逻辑关系：政府为储户提供保险导致银行破产。
此题不是GAP类型的assumption，因为推理没有明显的跳跃。
用取非的方式即可判断。D项取非后削弱了原推理，因为它直接否定了到导致银行破产的原因，给了一个新原因。
所以，此题找assumption的方法是排除它因。