Consider the function $g$ defined on $\mathbb { R }$ by:
$$g ( x ) = \frac { 2 \mathrm { e } ^ { x } } { \mathrm { e } ^ { x } + 1 } .$$
The representative curve of the function $g$ admits as an asymptote at $+ \infty$ the line with equation:\\
a. $x = 2$;\\
b. $y = 2$;\\
c. $y = 0$;\\
d. $x = - 1$