(2013·高考浙江卷)Half of ________ surveyed in 16 countries say they go first to their closest friend to share their deepest wishes and darkest fears.

A．these

B．some

C．ones

D．those

在玉米单交种F₂群体中，其株高的极端类型在F₂中占0.39％，因此，控制玉米株高的基因对数应该是（）。

A、5对

B、4对

C、3对

D、6对