题目

如图，在三棱锥中，平面，，现从该三棱锥的个表面中任选个，则选取的个表面互相垂直的概率为（ ）A. B. C. D. 答案：【答案】A【解析】根据线面垂直得面面垂直，已知平面，由，可得平面，这样可确定垂直平面的对数，再求出四个面中任选2个的方法数，从而可计算概率．由已知平面，，可得，从该三棱锥的个面中任选个面共有种不同的选法，而选取的个表面互相垂直的有种情况，故所求事件的概率为．故选：A．阅读理解Tomorrow is Children’ s Day. We are going to have a party in the park. I’m going to buy some flowers, balloons and gift with Miss Li.At the party, Nancy can play the music. Kelly can sing an English song. Kevin can sing a Chinese song. Mary and Amy can dance. And Jack can draw some beautiful picture.What can Sam do then? Sam can’t sing or dance. But he can take photos for us. He’s helpful, too.1. ________ is Children’s Day. （ ）A. Today B. tomorrow C. Tomorrow2. ________ can sing an English song. （ ）A. Kelly B. Kevin C. Kelly and Kevin3. Where are they going to have the party? （ ）A. In the school. B. In the park. C. In the garden.4. Can Sam dance at the party? （ ）A. Yes, he can. B. No, he can’t. C. We don’t know.