—Does your uncle still smoke?

—He       given it up. It’s two years ever since he      .

A．can’t have; smoked

B．may have; smoked

C．should have; has smoked

D．should have; didn’t smoke

离心泵的叶轮形式有（）。

A.闭式叶轮

B.半敞式叶轮

C.敞式叶轮