To Study Traffic Flow Along a Major Road, the City

Multiple Choice

To study traffic flow along a major road, the city installs a device at the edge of the road at 4:00 am. The device counts the cars driving past, and records the total periodically. The resulting data is plotted on a graph, with time (in hours) on the horizontal axis and the number of cars on the vertical axis. The graph is shown below. It is a graph of the function = Total number of cars that have passed by after t hours. When is the traffic flow the greatest?

A) At t=6 hours.
B) At t=3 hours.
C) At t=4 hours.
D) At t=5 hours.