Dear professor, Banks normally receive money from their customers in two distinct forms on current account, and on deposit account. With a current account, a customer can issue personal cheques. No interest is paid by the bank on this type of account. With a deposit account, however, the customer undertakes (答应) to leave his money in the bank for a minimum specified period of time. Interest is paid on this money. The bank in turn lends the deposited money to customers who need capital. This activity earns interest for the bank, and this interest is almost always at a higher rate than any interest which the bank pays to its depositors. In this way the bank makes its main profits. We can say that the primary function of a bank today is to act as an intermediary (中间人) between depositors who wish to make interest on their savings, and borrowers who wish to obtain capital. The bank is a reservoir (水库) of loanable money, with streams of money flowing in and out. For this reason, economists and financiers often talk of money being' liquid' , or of the ' liquidity ' of money. Many small sums which might not otherwise be used as capital are made useful simply because the bank acts as a reservoir. The system of banking rests upon a basis of trust. Innumerable acts of trust build up the system of which bankers, depositors and borrowers are part. They all agree to behave in certain predictable ways in relation to each other, and in relation to the rapid fluctuations of credit and debit. Consequently, business can be done and cheques can be written without visibly changing hands. On______, the bank will pay interest.