[单选题]
The variation of displacement of a trolley with time t is shown on the graph below.
The magnitudes of the instantaneous velocities of the trolley at times $t_1$ and $t_2$ are $v_1$ and $v_2$ respectively. Which of the following correctly compares the instantaneous velocities with the magnitude of the average velocity of the trolley for the whole of the motion shown?
A. $v_1$ is Greater than the average velocity;$v_2$ is Greater than the average velocity
B. $v_1$ is Greater than the average velocity;$v_2$ is Less than the average velocity
C. $v_1$ is Less than the average velocity;$v_2$ is Greater than the average velocity
D. $v_1$ is Less than the average velocity;$v_2$ is Less than the average velocity
