题目

His parents always make him     his homework for two hours. A. do    B. doing     C. to do     D. does 答案：A已知长方体ABCD-A1B1C1D1中，AB=BC=2，A1D与BC1所成的角为，则BC1与平面BB1D1D所成角的正弦值为（ ）A．B．C．D．