单选题 Of the following,_____ is not to be done when the engine is running.

单选题 At least _____ shall pass after the engine is stopped before you can open the crankcase cover for inspection.

单选题 In the indirect refrigerating system,cold brine and water are often used_____.

单选题 Passage 2

In addition to the main parts,there are a number of systems necessary for the operation of the engine,such a the starting system served by the air compressors and air bottles,the fuel-injection system with its camshaft drive, the cooling system and the lubricating system.Besides,the high pressure turbocharging system is also an important part to heavy engines.

The starting system is usually operated by the_____.

单选题 The working of the camshaft has much to do with the_____.

单选题 A medium to transfer heat between the refrigerant and the substance to be cooled exists in A:direct refrigerating system.

单选题 Passage 3

Special care should be taken to stop leaks of all descriptions immediately after they occur.Vital components of the engine should be frequently examined.The crankcase cover should never be allowed to open for investigation when the engine is running.And it should not be opened until at least fifteen minutes after the engine stops.Lights of high voltage or naked lights should never be used for fear of fire or explosion.

"Leaks of all description"in the passage means_____.

单选题 Passage 1

Mechanical refrigerating system can be divided into two classes:the direct one and the indirect one.In the  former,the refrigerant directly takes away the heat from the substance to be cooled.That is to say the heat exchange takes place directly between the surrounding substance and the refrigerant,while in the latter,cooling liquids,such as cold brine and water,are employed as a medium to carry out the transfer of heat between the refrigerant and the surrounding substance to be cooled.

In the refrigerating system,the refrigerant becomes after the heat exchange takes place.