The displacement-time graph of a moving particle with constant acceleration is shown in figure. The velocity-time graph is given by

At t=0, slope of the x-t graph is zero; hence, velocity is zero at t=0. As time increases, slope increases in negative direction; hence. velocity increases in negative direction. At point (1), slope changes suddenly from negative to positive value; hence, velocity changes suddenly from negative to positive and then velocity starts decreasing and becomes zero at (2). Option (a) represents all these clearly.