题目

完形填空 Sam is eleven years old. One day, his friend Tony says to him，“I am going to __  1___a birthday party on Saturday afternoon. Would you like___2__to my party?” “I’d love to,” answers Sam. Before Sam goes to the party __3__Saturday, his mother says to__4__, “When you go to the party, you must be polite (有礼貌的).Don’t ask for food until (到······为止) someone___5    it to you.” Sam answers,” All right, Mum.” Then Sam___6___to Tony’s house. There are___7___children at the party. They sing” Happy birthday to you” around the birthday cake. 直线a，b，c及平面α，β，下列命题正确的个数是（ ）①若a?α，b?α，c⊥a，c⊥b 则c⊥α     ②若b?α，a∥b  则 a∥α③若a∥α，α∩β=b  则a∥b               ④若a⊥α，b⊥α 则a∥b．A．4B．3C．2D．1