Everyone else was wearing a T-shirt,   __    ?               [ ]

A. were they        

B. wasn't he          

C. was he

下述关于泵的说法正确的是（）。

A．比转数是对所有泵分类的相似准则

B．允许吸入真空度大的泵自吸能力较强

C．凡是叶轮式泵皆不能作液压泵用

D．回转式容积泵只能作油泵用