题目

Toby was not able to solve the problem.It was too difficult. (as)（句子合并） 答案：As the problem was too difficult, Toby was not able to solve it.已知m、n是两条不重合的直线，α，β，γ是三个互不重合的平面，给出下列命题①若m∥β，n∥β，m，n?α，则α∥β②若α⊥γ，β⊥γ，α∩β=m，n?γ，则m⊥n③若m⊥α，α⊥β，m∥n，则n∥β④若n∥α，n∥β，α∩β=m，那么m∥n其中正确命题的序号是    ．