An economy can produce the following combinations of goods: 50x and 0y, 40x and 10y, 30x and 20y, 20x and 30y, 10x and 40y, and 0x and 50y. the production possibilities frontier (ppf) for the economy is: a. concave downward because the opportunity cost of producing the 10th unit of y isgreater than the opportunity cost of producing the first unit of y. b. a straight (downward-sloping) line because the opportunity cost of producing the twogoods is constant. c. concave downward because the opportunity cost of producing the 40th unit of y is lessthan the opportunity cost of producing the 10th unit of y. d. a straight (downward-sloping) line because the opportunity cost of producing the 10thunit of x is greater than the opportunity cost of producing the 40th unit of x. e. a straight (downward-sloping) line because the opportunity cost of producing the 30thunit of y is greater than the opportunity cost of producing the 30th unit of x.