单项选择题
A.gravity and feed oil cups
B.grease cups
C.hand during installation
D.leakage through the stuffing box
单项选择题 The steam coils in a high pressure evaporator used for saltwater service should be de-scaled with （）.
单项选择题 Which of the listed chemicals can be routinely used to maintain the hygienic quality of potable water?（）
单项选择题 The ratio of the weight of moisture contained in a given volume of air, to the weight of moisture that the same sample would hold if saturated, is called the（）.