单项选择题 The flash-evaporator is different with the submerged-tube evaporator in that for the former（）

单项选择题 Which one of the followings might not be employed to create vacuum for flash type evaporator? （）

单项选择题 The design of for a flash type evaporator is of critical importance because it must provide an optimum feedwater spray pattern that facilitates the flashing process, and it must also maintain a pressure differential between successive stages（）