Which of the following statements is correct? A. The income effect explains why a price change causes a movement along a given supply curve. B. The income effect explains why a price change causes the entire demand curve to shift to the right or to the left. C. The income effect explains why a price change causes a movement along a given demand curve. D. The income effect explains why a price change causes both the demand curve and the supply curve to shift to the night or to the left.