Mary is going _____ December, and she's staying _____ three weeks.     [ ]

A. on; for

B. in; for

C. at; in

D. in; on

当汽压升到0.3～0.4MPa时，应（）。

A.冲洗压力表存水弯管

B.冲洗水位表

C.排汽

D.给水和排污