Which of the Following Is True of Exchange

Which of the following is true of exchange?

A) The value of a good is determined by the cost of the resources required to produce the good.
B) Exchange makes it possible for trading partners to produce more goods through division of labor and adoption of mass production methods.
C) Nothing new is created by exchange; if one party to an exchange gains, the other must lose an equal amount.
D) Both a and b are true.