单项选择题
Although lube oils used in the main lubricating service systems should have a relatively high flash point to avoid ignition, they can create smoke and fire hazards when they （）.
A.are exposed to a vacuum B.come in contact with extremely hot surfaces C.are reduced in temperature to just above the pour point D.become extremely agitated or aerated
单项选择题 The viscosity of an oil is a measure of its （）.
单项选择题 The pour point of lubricating oils is affected the most by which of the following?（）
单项选择题 Which of the following statements is correct concerning the viscosity of lubricating oil?（）
