题目

When I came in, I saw him ______ in a chair deep in thought. A. sat   B. seated   C. seating    D. being seated 答案：B已知正四棱锥S-ABCD的侧棱长与底面边长都相等，E是SB的中点，则AE、SD所成的角的余弦值为（　　）A．13B．23C．33D．23