A.10mg/m3(15ppm) B.30mg/m3(20ppm) C.30mg/m3 D.15mg/m3(10ppm)
A.一級(jí) B.二級(jí) C.三級(jí) D.四級(jí)
A.30mg/m3(20ppm) B.20mg/m3(30ppm) C.3mg/m3(2ppm) D.2mg/m3(3ppm)