Answer
Graph "C" is the correct sketching.
Work Step by Step
For $y =−\sqrt{x},$
when $x=0, y=0$ and $x=4, y=−2$
The curve passes through $(0,0)$ and $(4,−2)$
Since the graph of $y=−\sqrt{x}$ is the same as the graph of $y=\sqrt{x}$ reflected across the x-axis, graph "C" is the correct sketching.