（）are used to digest the sewage to produce innocuous sludge in a biological sewage treatment plant.

To proceed to the assistance of a ship in distress is（）

A purge recovery system is used in a centrifugal air conditioning or refrigeration system to （）

Diesel engine air start system check valves are opened by （）

To shut down a diesel engine after it exceeds the set maximum speed，which type of device listed should be used?（）

If separating effect is not good, which measure should be taken （）

The condensers located in various stages of a flash evaporator are cooled by（）

The ISPS Code consists of a mandatory section-Part A, which shows（）

The treatment of the fuel oils involves storage, heating, filtering and（）

（）connectors hold best if a wire is accidentally pulled or a connection becomes loose.