能预防和治疗脚气病的维生素为（）。

A．V_pp

B．VB₁₂

C．VB₁

D．V_x

用in, on, under, behind 填空。

     I have a nice and clean room. There is a small desk __1__ the room. My clock is __2__ the desk.

The soccer is __3__ the bed. My backpack is __4__ the door of the room. My pen and eraser are not

__5__ the pencil-box. The pencil-box is not __6__ the backpack. It's __7__ the clock.