如果温度降到零下，排空水系统。
A When the temperature is below zero, depressurize the water system.
B If the temperature drops below zero, deflate the water system.
C If the temperature decreases to less than zero, drain the water system.
A When the temperature is below zero, depressurize the water system.
B If the temperature drops below zero, deflate the water system.
C If the temperature decreases to less than zero, drain the water system.