⑴若α⊥γ，β⊥γ，则α∥β
⑵若m⊥α，n⊥α，则m∥n
⑶若m∥α，n∥α，则m∥n
⑷若m∥α，m∥β，则α∥β
30＋40=____ 70－40=____ 20＋70=____ 80－10=____
Nobody knew who was the first ________ at school that morning when the window was broken.
