So, if you have never seem the graph of sqrt(x) before, you can find the solution through the following reasoning:
The 2 functions showm are inherently different in especially one aspect: The first one, let’s call it A, is only defined for all numbers equal or bigger than zero, whereas the second one, let’s call it B, is defined for all x-values.
Now, which of the is valid for f?
Try plugging in negative numbers (which only B can) and see what happens :)
Solution: A, as we are only allowed to plug in 0 or positive numbers into the square root (which is not defined for negative real numbers)