If $$f(x) = \frac{x}{x - 1}$$ then $$\frac{f(a)}{f(a + 1)} =$$

A

$$\frac{a^2}{a^2 - 1}$$

B

$$\frac{a^2}{a^2 + 1}$$

C

$$f(a^2)$$

D

$$f(a^3)$$