1. chemical composition of the comet 
   彗星化学组成
2. Recently they have discovered a comet. 
   最近我们发现了一颗彗星。
3. artificial fumigation for plants 
   植物人工熏气
4. artificial improvement forsoil mass 
   人工土质改良
5. artificial propagation of fish 
   鱼类人工繁殖

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