单项选择题
All items such as steam pipes, exhaust pipes and fittings which, because of their location and operating temperature, present a hazard should be adequately lagged.That means the items should（）
A.not be put into operation too early B.be pay adequate attention to C.be used only when necessary D.be coated with certain material
单项选择题 In machinery space, the valves, pipes should be（）
单项选择题 The guard, fencing or shielding for moving parts or machinery can be removed for repair only when the machinery it belongs to（）
单项选择题 Before starting an engine by air, the engine must（）
