From the given $v-t$ graph it can be inferred that the object is
$(a)$. in uniform motion
$(b)$. at rest
$(c)$. in non-uniform motion
$(d)$. moving with uniform acceleration
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In the given $v-t$ graph, it is a straight line parallel to $t-axis$ which indicates that the velocity is the same with respect to the time interval. So the object is moving in uniform motion.

So, option $(a)$ is correct.