单项选择题
When the propeller blades are integral with the hub, the propeller is called a （）.
A.built up propeller B.solid propeller C.controllable pitch propeller D.suction back propeller
单项选择题 The tendency of a flammable liquid to vaporize is indicated by its （）.
单项选择题 Moisture in the refrigerant may （）.
单项选择题 Why will a two stage flash type distilling plant tend to operate more efficiently when operating in cold seawater?（）
