单项选择题
The thermostatic valve has a throttling action, that is to say the valve can（）
A.stop the refrigerant from flowing B.force the refrigerant to flow C.cause the refrigerant pressure to rise D.cause the refrigerant pressure to fall
单项选择题 When the refrigeration demand is small,（）
单项选择题 When the heat load begins to increase, the needle valve of an expansion valve will（）
单项选择题 One of the main purposes of refractories in a boiler furnace is to（）
