a) If a vertical line is drawn from any point on the axis representing t, we see that it cuts the graph at two points which means the particle has two positions at the same instant of time which is not possible. So, the given x-t graph, shown in (a), does not represent the one-dimensional motion of the particle
(b)  If a vertical line is drawn from any point on the axis representing t, we see that it cuts the graph at two points which means the particle has two velocities at the same instant of time which is not possible. So, the given v-t graph, shown in (b), does not represent the one-dimensional motion of the particle.
(c) Speed has negative values in the graph which is not possible. So, the given v-t graph, shown in (c), does not represent the one-dimensional motion of the particle.
(d) The given v-t graph, shown in (d), does not represent the one-dimensional motion of the particle. This is because the total path length traveled by the particle cannot decrease with time.