Which of the following statements is CORRECT?

a$.$ If a firm increases its sales while holding its accounts receivable constant, then, other things held constant, its days' sales outstanding will decline.

b$.$ A reduction in accounts receivable would have no effect on the current ratio, but it would lead to an increase in the quick ratio.

c$.$ If a firm increases its sales while holding its accounts receivable constant, then, other things held constant, its days' sales outstanding $($DSO$)$ will increase.

d$.$ There is no relationship between the days' sales outstanding $($DSO$)$ and the average collection period $($ACP$).$ These ratios measure entirely different things.