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 （）.

单项选择题 Maintaining the lowest possible scavenging air temperature at all times is not recommended due to the possibility of the （）.

单项选择题 In any diesel engine closed freshwater cooling system, the lowest pressure exists at the （）.