题目

---Can you describe_______?    ---Of course. A. what the robber is like            B. how the robber is like C. what does the robber look like     D. how the robber looks like 答案：A如图所示，四棱锥P﹣ABCD中，AB⊥AD，AD⊥DC，PA⊥底面ABCD，PA=AD=AB= CD=1，M为PB的中点． （1）试在CD上确定一点N，使得MN∥平面PAD；（2）点N在满足（1）的条件下，求直线MN与平面PAB所成角的正弦值．