污水在格栅前渠道流速一般控制在（）。

A、0.4~0.5m/s

B、0.4~0.8m/s

C、0.6~0.8m/s

D、0.6~1.0m/s

A certificated lifeboatman assigned to command the lifeboat must（）.

A.be the first individual to board the craft

B.drain the hydraulic pressure before lowering the craft

C.have a list of the persons assigned to the lifeboat

D.All of the above