社会循环中所形成的（）和（）是天然水体最大的污染来源。
参考答案：生活污水；各种工业废水
各拉杆腐蚀、磨耗深度大于（）时须更换。
A.15％
B.20％
C.25％
D.30％
I am ______ the government as well as to the general public for just treatment ______ peasant-workers,
who have made great contributions to the improvement of city life. [ ]
A. asking; on behalf of
B. applying; in the name of
C. demanding; in the name of
D. appealing to; on behalf of
