c
(c) From given \(a - t\) graph it is clear that acceleration is increasing at constant rate

\(\therefore \) \(\frac{{da}}{{dt}} = k\) (constant) \(⇒\) \(a = kt\) (by integration)

\(⇒ \frac{{dv}}{{dt}} = kt\) \(⇒\) \(dv = ktdt\)

\(⇒ \int_{}^{} {dv} = k\int_{}^{} {tdt} \) \(⇒\) \(v = \frac{{k{t^2}}}{2}\)

i.e. \(v\) is dependent on time parabolically and parabola is symmetric about v-axis.
and suddenly acceleration becomes zero. i.e. velocity becomes constant.

Hence \((c)\) is most probable graph.