The middle term in the expansion of $$\left(1 - \frac{1}{x}\right)^n (1 - x)^n$$ in powers of $$x$$ is

A

$$-\,^{2n}C_{n-1}$$

B

$$-\,^{2n}C_n$$

C

$$^{2n}C_{n-1}$$

D

$$^{2n}C_n$$