废水和污泥二级处理的一个目的是（）。
A、提高氯含量
B、减少BOD
C、促进形成多氯联苯PCB
D、抑制氨化作用
参考答案：B
23. --- Where ____ the recorder? I can’t see it anywhere.
--- I ____ it right here. But now it’s gone.
did you put; have set up B. have you put; put
C. had you put; was putting D. were you putting; have put
