题目

AMERICANA HOTEL CRYSTAL CITY Convenient location 5 minutes from Washington D. C. and one block to Crystal City Metro (地铁), Crystal City Underground. Free parking, free deluxe continental breakfast and complimentary (收费的) hotel shuttle service to Ronald Reagan Washington National Airport. Phone (703) 979­3722 DAYS INN ARLINGTON Days Inn Arlington is located two miles from the Pentagon, Lincoln Memorial. There is a restaurant which serves American style food, plus two meeting rooms and an outdoor pool. Complimentary shuttle service runs to the Rosslyn Metro Station. Complimenta 已知a，b都是实数，那么“”是“”的   （    ）     A．充分不必要条件       B．必要不充分条件     C．充要条件     D．既不充分也不必要条件