A city planner is comparing traffic patterns at two different intersections. He randomly selects 12 times between 6 pm and 10 pm, and he and his assistant count the number of cars passing through each intersection during the 10 minute-interval that begins at the time. He plans to test the hypothesis that the mean difference in the number of cars passing through the two intersections during each of those 12 times intervals is 0. Which is the appropriate test of the city planner’s hypothesis?