If the Following Defines a One-To-One Function, Find Its Inverse $f(x)=\sqrt{x+9}$

Multiple Choice

If the following defines a one-to-one function, find its inverse. If not, write "Not one-to-one."
- $f(x) =\sqrt{x+9}$

A) $f^{-1}(x) =x^{2}-9, x \geq 0$
B) $f^{-1}(x) =\sqrt{x-9}$
C) Not one-to-one
D) $f^{-1}(x) =(x+9) ^{2}$