Mr．Smith is a good teacher except that he          some of his students by criticizing tbem whenever they make a mistake．

A．puts down

B．puts up

C．put s off

D．puts away

若单位时间内流过管道的流体数量是按照质量计算的，叫做（）。

A、体积流量

B、质量流量

C、能量流量

D、都不是