单项选择题 In engines with system, the lubricating oil can be added to the engine through the filling hole in the crankcase cover, by using a hand oil can, or through the separator pipe（）

单项选择题 Main engines as well as auxiliary engines operating on heavy fuel should have continuous on the lubricating oil, either according to the bypass or batch principles（）

单项选择题 These acid residues must be prevented from entering the crankcase, otherwise the lube oil would be（）