Flame failure in an automatically fired auxiliary boiler can from a/an （）

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

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

When does auxiliary burner of incinerator put into operation? （）Ⅰ. start incinerator when it is coldⅡ. the sludge for dealing with is littleⅢ. the sludge for dealing with is largeⅣ. the water and impurity in sludge are too muchⅤ. the temperature in incinerator is lowⅥ. dealing with little solid rubbish

If two A.C.generators are to be operated in parallel, the load is distributed evenly by（）

Thermostatic steam pressure reducing valves are used in the fuel oil service system to control the（）

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

Using a file without a handle may result in （）

“Insufficiency of manning or insufficiency of certification of seafarers” is an identification of a（）

The additional mark （）in the Classification Certificate for Machinery means propulsion apparatus is remotely controlled on the navigating bridge control station, and engine assembly control station is unmanned periodically.