The motion of a lift (elevator) in a shopping centre is given by the velocity-time graph below, where time `t` is in seconds, and the velocity of the lift is `v` metres per second. For `v > 0` the lift is moving upwards.
The graph shows that at the end of 30 seconds, the position of the lift is
A. 17.5 metres above its starting level.
B. 5 metres above its starting level.
C. at the same position as its starting level.
D. 5 metres below its starting level.
E. 17.5 metres below its starting level.