A student reviewing kinematics graphs for a body moving along a straight line writes four claims, labelled I to IV below. Identify which of the student's claims are physically correct.

• I. The area under a velocity-time graph over an interval equals the displacement in that interval.
• II. The slope of a position-time graph at an instant equals the acceleration at that instant.
• III. A body can have zero velocity and a non-zero acceleration at the same instant.
• IV. If the velocity and acceleration of a body have opposite signs, the body is speeding up.