The indicator constant for an acidic indicator, `HIn` is `5xx10^(-6)M`. This indicator appears only in the colour of acidic form when `([In])/([HIn])le(1)/(20)` and it appears only in the colour of basic form when `([HIn])/([In])le(1)/(40)` . The pH range of indicator is `[` Given `: log 5=0.7]`
A. 3.7-6.9
B. 4.0-6.6
C. 4.0-6.9
D. 3.7-6.6