You have noticed that your next-door neighbor, Mary, always works in the garden, and her husband, Joe, always walks the dog. You conclude that if Joe and Mary are efficient, then it must be the case that:

A、Mary'sopportunitycostofwalkingthedogislowerthanJoe's.;
B、Joeexperiencesincreasingopportunitycostswhenhegardens,butnotwhenhewalksthedog.;
C、Joehasacomparativeadvantageinwalkingthedog.;
D、Maryhasanabsoluteadvantageingardening.