－What did your parents think about your decision?

－They always let me do _____ I think I should. [ ]

A. when

B. that

C. how

D. what

国内负压原稳装置手动启动螺杆式压缩机后，应缓慢（），关小回流阀，压缩机加载。

A.打开压缩机出口阀

B.关闭压缩机卸载阀

C.关闭压缩机出口阀

D.打开压缩机卸载阀