磷酸盐加药点是（）。

A.20-50ug/L
B.10-50ug/L
C.20-40ug/L
D.15-50ug/L

A.100ug/kg ；50ug/kg
B.100ug/kg ；20ug/kg
C.100ug/kg ；30ug/kg
D.80ug/kg ；50ug/kg

A.5-10%
B.8-10%
C.6-8%
D.4-10%