— Your classroom looks bright and tidy.

— It        after school every day.

A．cleans

B．cleaned

C．is cleaned

D．was cleaned

已知某股票的必要收益率为12%，市场组合的平均收益率为16%，无风险报酬率为4%，则该股票的β系数为( )。

A．0.67

B．0.75

C．0.33

D．0.2