Fourier transform of $$te^{-at} u(t)$$, (where a > 0, u(t) is the Unit step function) is :

A

$$\frac{a}{(a + j2 \pi f)^2}$$

B

$$\frac{1}{(a + j2 \pi f)^2}$$

C

$$\frac{a}{(a + j2 \pi f)}$$

D

$$\frac{1}{(a + j2 \pi f)}$$