— Has your former classmate come back from America?

— Yes, he _______ there for eight years. [ ]

A. has stayed

B. stays

C. stayed

D. had stayed

柴油机增压器压气机喘振产生的原因之一是（）。

A.进气压力低

B.进气道堵塞

C.进气压力高

D.转速低