冰针属于（）现象。
A.降水
B.地面凝结
C.其它
参考答案：C
This is my twin sister, Lucy. Not only she but also I good at drawing.
A. is B. am C. are
计算二重积分[*]，其中D为y=x2，y=4x2及y=1所围成的闭区域．
