Consider two points on the PPF: point A, at which there are 10 apples and 20 pears, and point B, at which there are 7 apples and 21 pears. If the economy is currently at point A, the opportunity cost of moving to point B is __________.a. 1 pear. b. 7 apples c. 3 apples. d. 21 pears.