单项选择题 An excessive amount of water is prevented from entering a vessel using a water lubricated stern tube bearing by the use of the （）.

单项选择题 Under normal conditions, the refrigerant enters the compressor in an operating refrigeration system as a （）.

单项选择题 Some vessels are equipped with a water lubricated stern robeWhen at sea, operating under normal conditions, the water service valve from the ships saltwater system to the bearing should be （）.