单项选择题
A.单氟磷酸钠 B.氟化亚锡 C.氟化钠 D.氟化钙 E.氟化胺
A.1ppm B.10ppm C.100ppm D.1000ppm E.10000ppm
A.10ppm B.500ppm C.1000ppm D.10000ppm E.1ppm