一般生活污水在曝气池（）天左右就出现活性污泥絮体。
A.3；
B.7；
C.15；
D.30。
参考答案：B
The players ____ from the whole country are expected to bring us honor in this summergame. [ ]
A. selecting
B. to select
C. selected
D. having selected
阈强度
