Which statement(s) is/are true about the law of increasing opportunity cost?

a. Some resources and skills cannot be easily adapted from their current uses to alternative uses.

b. The more you produce of one good, the more you are forced to employ inputs that are relatively more suitable for producing other goods.

c. Resources tend to be specialized, so we lose some of their productivity when we transfer those resources from producing what they are relatively good at to producing something at which they are relatively bad.

d. All of these are true.