问题如下：
Jim, a junior economist, says “In comparison with barter transaction, the use of money is more efficient as a medium of exchange. However, it has a disadvantage that money supply should be under control, therefore a central bank is necessary for an economy.” Is Jim correct?
选项：
A.He is incorrect about comparison with barter transaction.
B.He is incorrect about disadvantage of money transaction.
C.Correct.
解释：
B is correct. Medium of exchange is one of the primary functions of money. It is widely accepted to pay for goods and service and more efficient than barter transaction. The existence of central bank is in recent centuries and it is not the disadvantage of money transaction.
考点：货币职能和中央银行
解析：交换媒介是货币的主要功能之一。人们普遍接受用现金支付货物和服务，这比以物易物更有效。中央银行的存在是近几个世纪的事，它不是货币交易的弊端。相反，其效管理可以加速交易的有效性。
“In comparison with barter transaction, the use of money is more efficient as a medium of exchange. However, it has a disadvantage that money supply should be under control, therefore a central bank is necessary for an economy.”
感觉答案的解释还是有点牵强。“ it has a disadvantage that money supply should be under control”，这里的it根据上下文不是指中央银行，应该是代替上文的主语“the use of money”。所以并不觉得这句话不对。
