Compute the derivative of the function $()=1+1$f$($x$)=$x$1$x$+1.$

Select one:

a$.$

$1(+1)21$x$($x$+1)2$

b$.$

$1(+1)21($x$+1)2$

c$.$

$1(+1)21($x$+1)2$

d$.$

$1(+1)2$