A particle starts from origin O from rest and moves with a uniform...

A. Acceleration = constant; $av \to t$ graph will be constant line parallel to time axis. Option $\left(A\right)$ is correct.
B. $v = u + at$ ; velocity vs time graph will be straight line passing through origin. Option $\left(B\right)$ is correct.
$u = 0;$ initially at rest
$v =$ at
C. $X = \dfrac{1}{2}a{t}^{2}$ (particle was initially at origin) $v \to t$ graph will be parabola passing through origin. Option $\left(D\right)$ is correct.