A student measures his pulse rate while he is watching television and records it. Next he walks to a friend's house nearby and when he arrives, measures and records his pulse rate again. He and his friends then decides to run to the mall a few blocks away. On arriving at the mall, the student measures and records his pulse rate once again. Finally, after sitting and talking for a half hour, the student measures and records his pulse rate for the last time. Which graph below best illustrates the expected changes in his pulse rate according to the activities described above?