Which of the following would be the be st application of principles regarding gift giving to customers?
选项：

A:Give gifts before doing business with a customer.
B:Determine the gift-receiving policy of the customer's company
C:Once begun, maintain a regular and consistent pattern of gift giving
D:Clearly explain the conditions you expect of the customer who accepts a gift.
E:Give a gift proportional to the sale you expect to make from the customer.