（） allows for expansion and water make up in the water cooli

What is head tank in the closed cooling water system used for?

A.for the release of air from the cooling water

B.providing expansion room for heated cooling water

C.a place for implementing water and water treatment agent

D.all of the above

One of the reasons that causes oil flowed from sludge outlet of a self-cleaning purifier is

A.seal water supply be cut off

B.make-up water supply be cut off

C.oil outlet valve closed or not open sufficiently

D.the flow rate of oil is too much

B

The world is not only hungry，it is also thirsty for water． this may seem strange to you，since nearly 75% of the earth is covered with water． But about 97% of this water is sea water．Man can only drink and use the other 3% fresh water that comes from rivers，lakes，under-ground and other places． And we cannot even use all of that，because some of this fresh water has been made dirty．

At the moment，this small amount(数量) of fresh water is still enough for us． However，our need for water is getting greater and greater． Only if we take steps to solve this problem now，we can get away from a serious world water shortage later on． The people of the world cannot have an enjoyable life without enough clean water．

On one hand we should stop wasting this little water of ours，on the other hand we should find ways to reuse it，but this has not been done widely．

Today，in most large cities，water is used only once and it then returns to the sea or runs into underground places．lf we can make it clean again，it can be used once more just as if it were fresh from a spring．

But even if large cities reuse its water，we still would not have enough in the future． Where．could we turn to next for water? To the ocean! How can we do to make use of this great a-mount of sea water? We can take the salt from the water to make it fresh．

So if we take all these steps，we'll be in no danger of drying up!

( )26． Why does the writer say that the world is thirsty for water?

A． The amount of fresh water is really very small．

B． The people of the world waste too much water．

C． The people of the world have to drink a lot of water every day．

D． There are too many people in the world needing water．

Since lubricating oils and jet fuels are acutely water critical，it is necessary to effect full line draining and mopping up of any water in tanks before loading ______．

A.purging with hydrocarbon gas

B.gas-freeing operations

C.maintaining an inert condition

D.full line draining and mopping up of any water

Because the circulating water is in a closed loop,_______is installed to cater for expansion and contraction of the water at different conditions of operation.

A.an expansion joint

B.a drain tank

C.a head tank

D.a contraction tank

The cooling liquid used for the cylinder may be referred to as _____.

A.jacket water

B.make-up water

C.boiler water

D.flushing water

The main propulsion diesel engine jacket water temperature rises above normal, with the raw sea suction and the expansion tank water level being normal. Which of the following problems is most likely the cause?

A.Faulty thermostatic bypass valve

B.Eroded zinc pencils in the heat exchanger

C.Steam formation in the expansion tank

D.Excessive leakage from jacket water pump seals

29． The writer thinks that people in large cities should __________ ．

A． stop the used water from getting into underground

B． only use the water from the rivers

C． make their used water clean again

D． use as much sea water as possible

_____ allows for expansion and water make up in the water cooling system.

A.A top tank

B.A head tank

C.A head valve

D.A drain tank

The international shore connection ______．

A.Allows hook up of fire fighting water from shore facilities

B.Satisfies pollution prevention requirements

C.Allows emergency use of the fire main for deballasting

D.Permits discharge of waste oil to shore facilities