The slope of a producer's production possibilities frontier (when you ignore its negative sign):

a) gives the opportunity cost of the good measured on the horizontal axis

b)gives the reciprocal of the opportunity cost of the good measured on the vertical axis

c) is usually assumed to be increased when the output of the good measured on the horizontal axis increases (This assumption is called Increasing Opportunity Costs or Diminishing Returns)

d) all of the above answers are true