单项选择题
A.150mg/m3(100ppm) B.135mg/m3(90ppm) C.75mg/m3(50ppm) D.30mg/m3(20ppm)
A.大于 B.等于 C.小于 D.小于或等于
A.10mg/m3(15ppm) B.30mg/m3(20ppm) C.30mg/m3 D.15mg/m3(10ppm)