单项选择题 The outlet from an expansion tank of a closed freshwater cooling system should be piped to the （）.

单项选择题 Passages are drilled in the crankshafts of diesel engines to provide lubricating oil to the （）.

单项选择题 After a normal, or safety shutdown, automatic combustion control systems for an auxiliary boiler are designed to prevent the immediate refiring of a burner in order for the （）.