<正>Ⅰ.选择填空(15 分)21. Mr and Mrs Smith took a taxi to the airport to_their son_.A. see; off B. send; away C. show; out D. send; for22. He didn't work out the problem_I explained how to.A. except B. until C.when D.once23. -They used to be good friends but now they are like strangers. -How_this_?A. was; come about B. did; come aboutC. was; taken place D. does; happen