(N/A) The velocity-time $(v-t)$ graphs for motion with constant acceleration are as follows:
$(a)$ An object is moving in a positive direction with a positive acceleration.
$(b)$ An object is moving in a positive direction with a negative acceleration (deceleration).
$(c)$ An object is moving in a negative direction with a negative acceleration.
$(d)$ An object is moving in a positive direction until time $t_{1}$,then it turns back and moves with the same negative acceleration.
An interesting feature of a velocity-time graph for any moving object is that the area under the curve represents the displacement over a given time interval.