The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about______________?

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The amount of residual chlorine left in public water supply for safety against pathogenic bacteria is about______________?

A. 0.01 to 0.05 ppm
B. 0.05 to 0.5 ppm(Correct)
C. 0.5 to 1.0 ppm
D. 1.0 to 5.0 ppm