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 has an absolute advantage in gardening. b. joe has a comparative advantage in walking the dog. c. mary does not understand the principle of low-hanging fruit d. joe experiences increasing opportunity costs when he gardens, but not when he walks the dog.