— Alvin，are you coming with us?

—I'd love to，but something unexpected ________.

A．has come up

B．was coming up

C．had come up

D．would come up

流量计主要有（）式流量计，转子流量计和椭圆齿轮流量计。

A、差压

B、电磁

C、孔板

D、浮力