The term independent of x in the binomial expansion of $$\left(x - \frac{1}{x^2}\right)^3n$$ is

A

$$(3n)C_{2n}$$

B

$$(3n)C_{n}$$

C

$$(-1)^n . (3n)C_{2n}$$

D

$$(-1)^n . (3n)C_{n}$$