由于“赤潮”的影响，一条4千克重的草食性海洋鱼死亡，食物利用率按20%计算，该杂食鱼从出生到死亡，共需海洋植物千克。-七年级生物

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• —What______itbe? —It_______beacar,foritisnotmoving.Itbeahouse.[ ]A. must,mustn't,canB. can,can,
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• 农田中除草的目的是[]A．调节农田中生态系统的结构B．调节农田中生态系统的物种C．调节农田中生态系统的能量流动D．A和B-八年级生物
• 根据生态系统的有关知识，试分析回答下题：传统的“桑、蚕、鱼”农业结构，发展成了“桑、蚕、气、鱼”的新型农业结构。目前，我国劳动人民就学会了用桑叶喂蚕、蚕沙（蚕粪）养鱼、-七年级生物
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