Answer
$\bf{Graph (b)}$
Work Step by Step
The anti-derivative for $\dfrac{dy}{dx}=-x$ is $y=-\dfrac{x^2}{2}+C$
Plug $x=1,y=1$ in above equation $y=-\dfrac{x^2}{2}+C$ for solving the value of $C$.
Thus, $C=\dfrac{3}{2}$
Hence, $y=-\dfrac{x^2}{2}+\dfrac{3}{2}$;
This shows that a $\bf{Graph (b)}$with a concave down parabola.