清理过滤器时先打开过滤器的排污阀，然后打开过滤器上的（）。

A、挡板阀

B、针形阀

C、引压阀

D、放气阀

In heavy seas you decide to heave to. The lifeboat should be（）.

A.brought to a position with the stern into the seas

B.allowed to take its own head

C.brought to lay in the trough

D.brought bow into the seas