单项选择题
The extended aeration process consists of （） the liquor either by bubbling air through it or by agitating the surface.
单项选择题 A number of biological sewage treatments plants are in use at sea but nearly all work on the principle called （）
单项选择题 Which of the following would not be burnt in an incinerator on board?（）
单项选择题 During waste clothes being charged into an incinerator, the auxiliary burner（）.
