题目

— Do you know the ________ of the boys' 100-meter race?— Yes. A boy from Class 4 got the first place. A . picture B . problem C . rule D . result 答案：D如果两个相交平面都垂直于第三个平面，那么它们的交线垂直于第三个平面.已知α⊥γ,β⊥γ,α∩β=l.求证：l⊥γ.