The distance vs. time graph of a car moving at constant speed should be a straight line. why do the data points in the graph plotted from observing the motion not fall right on the line? a. the distance is not exactly proportional to time even if the speed is exactly constant. b. the distance and time are proportional only if the correct units of meters an seconds are used. c. data points can never look like they fall right on a straight line. d. the measurements are inexact.