A:①④
B:②③
C:②④
D:①③
--- Is that man Mr. Smith?
--- It ______ be him. He has gone to NewYork on business.
— What _______ they ________?
— They are farmers.
①商品和货币是一对孪生兄弟 ②货币是商品交换长期发展的产物
③货币是一种特殊的商品 ④先有商品,然后才有货币