They may be happy because their work provides a lot of pleasure.()
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Most environmental problems are caused by people.()
The lost bell is found in the parents' bedroom.()
EDTA同阳离子结合生成
A. 整合物
B. 聚合物
C. 离子交换剂
D. 非化学计量的化合物
E. 水合物
Parents can not hear the sound of the sleighbell.()
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