理财规划师预计某只股票呈现10%的收益率的概率是0.5，出现20%收益率的概率是0.2，而出现-5%的收益率的概率是0.3，那么该资产收益率的数学期望值是（）。

A.0.25

B.0.075

C.0.5

D.0.3

— May I tell this to my close friend?  

— No, you___________. Never let anybody else know about it.                     

A．needn't

B．shouldn't

C．mustn't

D．can't