离心泵运转时，如果泵内没有充满（），虽然叶轮转动，却不能输送液体
A.液体
B.气体
C.气液混合液
D.低于饱和蒸汽压的液体
参考答案：A
仿照例句用所给的词汇造句。
例：I, do my homework, last night
I was doing my homework last night.
A. they, have a dress rehearsal, yesterday evening
B. my grandma, visit my family, half an hour ago
C. I, travel in the south, at this time last year
D. they, build a power station, at that time
Customs vary greatly _______ country to country.
A．from
B．at
C．for
D．with
