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问题 单项选择题

利用带电粒子在电场作甩下定向移动的特性，对混合物组分进行分离、纯化和测定的技术为

A．电泳技术

B．电化学技术

C．层析技术

D．超速离心技术

E．光谱技术

答案

参考答案：A

选择题

Ten years ago the population of our village was _____that of theirs. [ ]

A. as twice large as

B. twice as large as

C. twice as much as

D. as twice much as

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单项选择题

城市与乡村的基本区别有许多方面，其主要差异之中不包含( )。

A．集聚规模差异
B．生产效率差异
C．物质形态差异
D．环境观念差异
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