Answer:
all positive real numbers and 0
Explanation:
The function has a square root in the x value, so this function can't have negative values, because a negative value of x would give a complex number for f(x), and positive values of x gives positive values of f(x).
The function f(x) can be zero, if the value of x is zero:

So the function f(x) can only have positive values and the value 0.
Correct option: "all positive real numbers and 0"