问题：
[单选] Here some oil in the oily water separator, as a result of its lower （）, will separate and rise into the oil collection space.
temperature。viscosity。density。velocity。
问题：
[单选] High-speed rotating in a centrifugal purifier can produce a force （） larger than the force of gravity.
many thousand times。between times。one time。at time。
问题：
[单选] If （） are taken at regular intervals, any unequal distribution of load will be easily found out.
differential of crank-webs。indicator diagrams。lube oil reading out。misalignment of crank-throw。
问题：
[单选] Of a kind of liquid is used to cool the diesel engine, it is invariably called （）
lubricant。coolant。combustion product。second refrigerant。
问题：
[单选] If diesel oil in this tank is used, the （） of the oil must not exceed 120 degree F.
viscosity。flash point。acid value。temperature。
问题：
[单选] If the atomizer holes are enlarged beyond the makers recommended size, the atomizer must be （）.
repaired。replaced。replenished。repeated。
问题：
[单选] If the engine （） for a long period, there will be a danger of frost.
must to stand inoperative。has to stand inoperative。must be stood idle。will stand idle。
问题：
[单选] If the engine does not start on air, it may be due to （）
low compression of the fuel pumps。incorrect timing of fuel pumps。the starting air valves stuck。air-locks in fuel oil pipeline。
问题：
[单选] If the engine does start on air, but combustion does not immediately begin, the cause may be （）.
failure of the fuel pumps。starting air pressure too low。stop valve in air line closed。the turning gear still engaged。
问题：
[单选] If the engine does start on air, but combustion does not immediately begin, the cause may not be （）.
low compression。failure of the fuel pump to discharge fuel。incorrect timing of fuel pump。turning gear being still o。
