单项选择题
When adding oil to a refrigeration system, precautions must be taken to ensure that （）.
A.the compressor suction pressure is not too high B.all air is purged from the pump and charging fittings C.the high pressure cutout switch is held open to prevent accidental starting D.the condenser is completely shutdown first
单项选择题 In a refrigeration system, if the cooling water to the condenser fails, the（）.
单项选择题 Accidental flooding of the engine room bilges by the bilge main is prevented by （）.
单项选择题 Zinc rods are installed in the refrigeration system （）.
