In Spearman rank correlation coefficient $$r_s = 1 - \frac{6 \sum d^2}{n(n^2 - 1)}$$, the maximum value of $$\sum d^2$$ in case of untied ranks is:

A

$$\frac{1}{2}(n^2 - 1)$$

B

$$\frac{1}{4}n(n^2 - 1)$$

C

$$n$$

D

$$\frac{1}{3}n(n^2 - 1)$$