The basic process of biological sewage treatment consists of the liquor either by bubbling air through it or by agitating the surface（）

A.any requirement appointed by the Officer
B.the most suitable requirement
C.the most stringent requirement
D.no requirement

A.plastics
B.comminuted or ground papers, rags, glass, metal etc
C.food waste comminuted or ground
D.Incinerator ash

A.gravity separation
B.use of adsorbents
C.use of flocculents
D.use of chemical addition