单项选择题

The materials cycle is a system that involves interactions and exchanges among materials, energy, and the environment.

A.正确
B.错误
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单项选择题
The smart materials can respond to the environmental changes.
A.正确
B.错误
单项选择题
2．设集合X={a，b，c}，下列集合不是X的划分的是 A {{a},{b},{c}} B {{a,b},{b,c}} C {{a,b},{c}} D {{a,b,c}}
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