单项选择题
A.[C]>2% B.[C]>4.3% C.[C]<2% D.[C]<4.3%
A.1.7% B.0.77% C.0.077% D.0.21%
A.668mm B.768mm C.868mm
A.危险源B.安全隐患C.不安全隐患
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