The graph shows speed versus time.
Section C happens between sections B and D.
In section B, the line is horizontal. The car is at a constant high speed.
In section D, the line is also horizontal. The car is at a constant low speed.
In section C, the line goes down to the right. It goes from the constant high speed of section B to the constant low speed of section D. In section C the car slowed down.
Answer: His car is slowing down.
