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问题 多项选择题

通风安全仪器仪表要有（）制度，按规定进行校正和检定，保证完好。

A.保管

B.维修

C.维护

D.保养

答案

参考答案：A, B, D

选择题
He is known _____ his being on time, so we don’t know the reason ____ his being late this time.
A．for; ofB．as; forC．for; forD．of; of
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单项选择题

沉淀IgM所用PEG6000浓度为（）

A.3%～4%

B.6%～7%

C.8%～12%

D.12%～15%

E.25%
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