单项选择题
A.5 B.10 C.15 D.20
A.0.949---0.954 B.0.948---0.954 C.0.949---0.953
A.N/20m B.N/100cm C.N/1200cm D.N/100m
A.23±0.2 B.23±0.1 C.24±0.1 D.都不对
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