单项选择题
A.≥20mm B.≥30mm C.≥40mm D.≥50mm
A.0.9 B.1.05 C.1.2 D.1.5
A.0.5-1.0m B.0.8-1.5m C.1.0-2.0m D.1.5-2.5m
A.15mg/m3 B.20mg/m3 C.25mg/m3 D.30mg/m3
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