题目

B Modern Manners Philip Howard answers your questions on contemporary etiquette (礼仪) Philip Howard, When my friend and I (two ladies of a certain age) go out to have a meal, she always leaves an extremely large tip. At times, the tip will equal the amount of one of the main dishes—sometimes it comes to about 30 per cent of the bill. I feel 15—20 per cent is adequate for services offered and depending on the type of restaurant. At a cafe I would like to leave 15 per cent or a bit more depending on the service and etc. A larger tip would be appropriate if we are in a big city or a nicer 27、如图，AD∥BC，BD平分∠ABC．求证：AB=AD