单项选择题 In a compression refrigeration plant the refrigerant flows from the expansion valve and through the （） where it absorbs heat from the space being cooled and becomes a gas or vapor.

单项选择题 Since heat will not flow freely from a body at a （） temperature to another at a （） temperature, it is necessary to expend mechanical work, heat, or electrical energy from an external source to achieve refrigeration.

单项选择题 In the process of （）, liquid changes into gas.