证明人可以在头脑中对客体的表象进行操作的实验是（）。
A.心理旋转实验
B.三山实验
C.罗森塔尔实验
D.感觉剥夺实验
参考答案：A
— How do you like your English teacher?
— He is great. We _____ friends since three years ago. [ ]
A. were
B. have made
C. have been
D. have become
(Ⅰ) 将累次积分
化成定积分，其中a＞0为常数； (Ⅱ) 求
．
化成定积分，其中a＞0为常数；
．