—What do you think your life will be like________ twenty years?

—Yeah.I have thought about it________ three years.

A．before;of

B．after;in

C．in;for

D．for;for

回归系数和相关系数的符号是一致的，其符号均可用来判断现象（）

A.线性相关还是非线性相关

B.正相关还是负相关

C.完全相关还是不完全相关

D.单相关还是复相关