A、A porter. B、A waitress. C、A nurse. D、A taxi-driver. C综合理解题。在A tip expected by the porter...，by taxi drivers...and by those who

Americans are big tippers. Generally the custom is more common in a large city than in a small town. Customers are expected to give a tip, or small amount of money, whenever services are performed. A tip is expected by the porter who carries your baggage, by taxi drivers (in the case, 15 percent of the fare) and by those who serve you in hotels and restaurants. For example, in hotels it is customary to give a tip to the porter who carries your suitcase and shows you to your room. In this case, 50 cents for each bag is satisfactory; in restaurants you generally leave about 15 percent fit. he bill on the table as a tip for the person who has served you.
    There are two common explanations for the origin of tipping. The Oxford English Dictionary says 6p is 17th century’ underworld slang for "give"—as in the threat "tip me your wallet or your life". Opponents of tipping will probably prefer this explanation and they argue that tipping suggests the practice that is originally a form of theft or robbery. The second explanation which is still less reputable is that in Renaissance coffee-houses, boxes were set near the door, into which customers could drop small sum of money for good service. These boxes, according to the story, bore the explanatory words "To Insure Promptitude", which was gradually shortened to Tip.