阅读理解。 Canadians and Americans usually tip in places like restaurants, airports, hotels and hair salons because many people who work in these places get low salaries. A tip shows that the customer is pleased with the service. At airports, porters usually get a dollar tip for each bag. Hotel bellhops (男侍) usually get a dollar for carrying one or two suitcases. A hotel door attendant (服务生) gets about a dollar for getting a taxi for people. Many people also tip hotel room attendants, especially when they stay in a hotel for several days. They usually leave a dollar for each day. The usual tip for other kinds of services--for example, for taxi drivers, barbers, hairdressers, waiters and waitresses-is between 10 and 20 percent of the bill. The size of the tip depends on how pleased the customer is. In most restaurants, the check does not include a service charge. If the group is large, however, there may be an added service charge. There is no tipping in cafeterias (自助食堂) or fast-food restaurants. 1. In the countries mentioned people tip usually to _____. [     ] A. express their satisfaction B. show their support C. encourage better service D. show off 2. What tip should you at least leave for a $50 restaurant check? [     ] A. $25 B. $5 C. $10 D. $15 3. In _____ you don't have to tip. [     ] A. a hotel B. a barber shop C. a McDonald's restaurant D. a restaurant