Analysis:

Deposit business is a business in which commercial banks absorb funds from the society at a certain interest rate and term, and repay the principal and interest according to regulations. This is the basic business of banks. Without deposits, there will be no sufficient funds and foundation to carry out business, and there will be no commercial banks. A meets the meaning of the question and should be selected; Loan business is the main business of commercial banks. No, neither C nor D, so the answer is A.