For ab ≠ 0. if * is defined by $$a * b = \frac{a^2 + b^2}{ab}$$ then $$\frac{(1 * 2) * (2 * 1)}{(1 * 3) + (3 * 1)} =$$

A

$$\frac{1}{5}$$

B

$$\frac{3}{10}$$

C

$$\frac{5}{4}$$

D

$$\frac{20}{3}$$