降水的反射率因子回波大致可分为（）三种类型。
A.积云降水回波
B.卷云降水回波
C.层状云降水回波
D.积云层状云混合降水回波
参考答案：A, C, D
绕某一定点旋转任意一个角度后，旋转后的图形仍与原图形重合，这个图形是[ ]
A．等边三角形
B．正方形
C．正六边形
D．圆
— My pet dog is ill and I have to take him to see a doctor.
— _____[ ]
A. Is that true?
B. It doesn't matter.
C. Oh, that's too bad!
D. Why?
