单项选择题
A.secure and tag the electrical circuit
B.place a crow bar in the flywheel of the unit
C.inform all persons in the area not to start the unit
D.make a log book entry
单项选择题 One of the main differences between the various types of screw pumps is in the （）.
单项选择题 The temperature at which water vapor in the atmosphere begins to condense is called the （）.
单项选择题 The tendency for lubricating oil to thin out at high temperatures and thicken at low temperatures will be characterized by a （）.