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 through x=0 moving in the positive x−direction with a constant speed . The position of the first body is given by x1(t) after time ‘t’, and that of the second body by x2(t) after the same time interval . which of the following graphs correctly describes (x1−x2) as a function of time ‘t’ ?