Maximum permissible residual chlorine in treated water should be ____________ mg/litre?
A. 0.001 to 0.01
B. 0.2 to 0.3
C. 2 to 3
D. 5 to 10
A. 0.001 to 0.01
B. 0.2 to 0.3
C. 2 to 3
D. 5 to 10