---I rang you yesterday afternoon. A man answered, but I didn’t recognize the voice.

--- Oh, it ____ my uncle. He was in my room then.

A．must have been

B．should have been

C．must be

D．should be

与疏水器的设计排水量有关的参数，是下列哪几项

A．疏水器阀孔直径

B．疏水器前后压差

C．疏水器选择倍率

D．疏水器的背压