单项选择题
In machinery space, the valves, pipes should be（）
A.arranged as close to each other as possible to save space B.arranged far away from each other for convenient operation C.be fixed or clamped to avoid vibration D.kept easy removable as to convenient repairing work
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（）
单项选择题 The oil pressure and flow from each bearings can be checked when（）
