题目

—Tom，have you ever watched the talent show The Voice of China? —Yes，Lucy，if you are good at singing，you may consider __ _ a try. A．to have  B．having  C．has  D．have 答案：B如图，在直三棱柱ABC-A1B1C1（侧棱和底面垂直的棱柱）中，平面A1BC⊥侧面A1ABB1，AB=BC=AA1=3，线段AC、A1B上分别有一点E、F且满足2AE=EC，2BF=FA1．（1）求证：AB⊥BC；（2）求点E到直线A1B的距离；（3）求二面角F-BE-C的平面角的余弦值．