单项选择题 As the refrigerant passes through the valve orifice, its pressure is reduced and part of the refrigerant turns into （）.

单项选择题 Freon 12 which is used to produce intense cold is normally a （） when at atmospheric pressure and temperature.

单项选择题 The quantity of cooled air delivered by an air conditioning unit should （） the sum of the quantity of air re-circulated to the unit and the quantity mechanically exhausted.