单项选择题
A.10g/L~15g/LB.20g/L~30g/LC.35g/L~45g/LD.60g/L~70g/L
A.介体传播B.非介体传播C.外力传播D.自然传播
A.10min---12minB.15min---20minC.25min---30minD.30min 以上