题目

 Could we put off the meeting? she asked.   ___________,he answered politely. This is the only day everyone is available.  A. Not likely    B .Not exactly   C. Not nearly        D. Not really 答案：A已知直线m⊥平面α，直线n在平面β内，给出下列四个命题：①α∥β⇒m⊥n；②α⊥β⇒m∥n；③m⊥n⇒α∥β；④m∥n⇒α⊥β，其中真命题的序号是    ．