问题
选择题
Bob saw a man _____ a little boy with his car in the street yesterday.[ ]
A. write down
B. knock down
C. fall down
D. climb down
答案
答案：B
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Bob saw a man _____ a little boy with his car in the street yesterday.[ ]
A. write down
B. knock down
C. fall down
D. climb down
答案：B
以下是空气污染指数与质量级别、质量状况的对应关系：
| 空气污染指数 | 0～50 | 51～100 | 101～200 | 201～300 | ＞300 |
| 空气质量状况 | 优 | 良 | 轻度污染 | 中度污染 | 重度污染 |
| 空气质量级别 | I | II | III | IV | V |
A．I级 优
B．II级 良
C．III级 轻度污染
D．V级 重度污染