Let's say, your raw water alkalinity increased from 230 mg/l to 235 mg/l and the pH to 7.9. Your chlorine residual then dropped below acceptable limits. What is the most likely cause of this condition?

a. Excess alkalinity reacted with the chlorine.

b. Chlorine has been converted to hypochlorous acid.

c. Chlorine has reacted with mineral compounds that raised the pH.

d. There has been an increase in hypochlorite.