A/O法中A池获得良好脱氮效果的必备条件有（）
A.好氧
B.缺氧
C.充足碳源
D.微量碳源
参考答案：B, D
The city is believed over by sandstorms from AD200 to AD400.
A．to cover
B．to be covered
C．to have been covered
D．that was covered
常用的膜剂材料（）
A.聚乙烯醇
B.胆固醇
C.二甲硅油
D.可可豆脂
E.EUDRAGIT
