Which function has an inverse that is also a function?
A$f(x)=x^2+2$
B$f(x)=2$
C$f(x)=2 x$
D$f(x)=2 x^2$
A$f(x)=x^2+2$
B$f(x)=2$
C$f(x)=2 x$
D$f(x)=2 x^2$