— I think it's going to rain.

— ________ The skies are dark and cloudy.  [      ]

A. Not really.  

B. I guess so.

C. Why not?  

D. How great!

计算简单相关的相关系数的要求是（）

A.因变量是正态变量，自变量可以不满足正态

B.自变量是正态变量，因变量可以不满足正态

C.两变量都要求满足正态分布

D.两变量只要求是数值变量指标

E.两变量只要求是分类变量指标