A particle is moving along the curve $x=a t^2+b t+c$. If $a c=b^2$, then the particle would be moving with uniform

rotation velocity acceleration retardation

acceleration

We have, $x=at^2+bt+C$ $\Rightarrow \frac{d x}{d t}=2 a t+b \text { and } \frac{d^2 x}{d t^2}=2 a$ $\Rightarrow \frac{d^2 x}{d t^2}$= constant.