Answer: Choice C
The x input of a square root function can be 0 or larger. If you take the square root of a negative number, then you'll get a complex number as a result. So we restrict the domain so that y is a real number.
We can say [tex]x \ge 0[/tex] or we can write what choice C shows to be more thorough, but they mean the same thing.
note: [tex]0 \le x < \infty[/tex] converts to the interval notation [tex][0, \infty)[/tex]
