Which statement is correct?

a. The term comparative advantage means: Having the ability to produce something with fewer resources (or to accomplish a task in fewer hours) than someone else.

b. The term comparative advantage means: Having the ability to produce something (or to accomplish a task) at a lower opportunity cost than someone else.

c. Workers who lack comparative advantage in what they do should be trained to improve their skills.

d. Workers who lack comparative advantage in what they do should be fired.