Figure 19-6 A graph of Q versus L shows a straight line, D 1, decreasing linearly, a second straight line, D 2, decreasing linearly to the right and parallel to D 1, and a third straight line, S, increasing linearly. Refer to Figure 19-6. Which of the following events would most likely explain a shift of the labor demand curve from D 2 back to D 1 ? a. The price of automobiles decreased. b. A large number of immigrants entered the automobile-worker market. c. The demand for automobiles increased. d. A technological advance increased the marginal product of automobile workers