单项选择题
A.阈限值 B.安全临界浓度 C.危险临界浓度 D.30mg/m³(20ppm)
A.最小 B.最大 C.临界 D.危险
A.150mg/m3(100ppm) B.135mg/m3(90ppm) C.75mg/m3(50ppm) D.30mg/m3(20ppm)