A body is at rest at x = 0, at t = 0, it starts moving in the positive X - direction with a constant acceleration. At the same instant, another body passes to x = 0 moving in the positive X - direction with a constant speed. The position of the first body is given by $x_1\left(t\right)$ after time t and that of the second body by $x_2\left(t\right)$ after the same time interval. Which of the following graph correctly describes $(x_1-x_2)$ as a function of time?