The unit step responseof a system with the transfer function $$G(s)=\frac{1-s}{1+s}$$ s given by which of the following? (A unit step function is represented by u(t))

A

$$(1-2e^{-t}) u(t)$$

B

$$(1-e^{-t}) u(t)$$

C

$$e^{-t} u(t)$$

D

$$2 e^{-t} u(t)$$