单项选择题
Under normal conditions, the quantity of air circulation becomes less and less.What is the reason?（）
A.dirty delivery ducts B.too much refrigerant C.the fouling filters D.high temperature outside
单项选择题 （）is used in typical marine pattern self-contained unit.
单项选择题 Which one is not the component of a typical, marine pattern self-contained unit?（）
单项选择题 With ducted air conditioning systems, the modern tendency is to use（）
