二次污染
参考答案：
由于某些原因，使已经转移的污染物又返回原来的环境中时，即造成二次污染。
You _______ to the meeting this afternoon if you have something important to do.[ ]
A. needn't to come
B. don't need come
C. don't need coming
D. needn't come
有利于水稻生产的气候条件是： [ ]
A、雨热同期
B、温和湿润
C、高温少雨
D、寒冷干燥
