单选题 What is the basis for the banking system?

A、 Contract system that can be enforced.
B、 People's willingness to deposit money in banks.
C、 The possibility that the bank can make profits from its borrowers.
D、 The fact that some people have surplus money while some need loans.

【正确答案】 A

【答案解析】根据第五段第二句可知银行体系的基础就是银行与其客户之间的协议可以得到执行，选A。