Let $$f(x) = \int_0^x (t + \sin(1 - e^t))dt$$, $$x \in \mathbb{R}$$. Then, $$\lim_{x \to 0} \frac{f(x)}{x^3}$$ is equal to

A

$$-\frac{1}{6}$$

B

$$\frac{2}{3}$$

C

$$-\frac{2}{3}$$

D

$$\frac{1}{6}$$