The graph shows a journey in a car. Which of the statements most likely describes the journey back to the starting point at the portion of the graph labeled O?
A The car travels different distances per unit of time, because the portion shows a linear, decreasing function.
B The car travels the same distance per unit of time, because the portion shows a linear, decreasing function.
C The car travels the same distance per unit of time, because the portion shows a nonlinear, decreasing function.
D The car travels different distances per unit of time, because the portion shows a nonlinear, decreasing function.