【单选题】Both Bill and Mary produce t-shirts and hats. If Bill’s opportunity cost of 1 t-shirt is 4 hats and Mary’s opportunity cost of 1 t-shirt is 3 hats, then
A.
Bill has a comparative advantage in the production of t-shirts.
B.
Mary has a comparative advantage in the production of t-shirts.
C.
Mary has a comparative advantage in the production of hats.
D.
Bill has a comparative advantage in the production of both t-shirts and hats.
【单选题】Bill:So MarY,how’S the coffee maker‘working?Mary:Actually,it doesn’t work well. Bill:Why don’t you take it back?Mary:__________,but I‘ve misplaced the receipt.