The basic function of money is the enable buying to be separated from selling, thus permitting trade to take place without the so-called double coincidence of barter. If a person has something to sell and wants something else (1) return, it is not necessary to search for someone able and (2) to make the desired exchange of items. The person can sell the (3) item for general purchasing power-that is, "money"-to anyone who wants to buy it and then use the proceeds to buy the desired item from anyone who wants to sell it. The importance of this function of money is (4) illustrated by the experience of Germany just after World War II, (5) paper money was (6) largely useless because, despite inflationary conditions, price controls were effectively (7) by the American, French, and British armies of occupation. People had to (8) to barter or to inefficient money substitutes. The result was to cut total output of the economy in half. The German "economic miracle" just after 1948 reflected partly a currency reform by the occupation authorities, (9) some economists hold that it stemmed primarily from the German government’s (10) of all price controls, (11) . permitting a money economy to (12) a barter economy. (13) of the act of sale from the act of purchase (14) the existence of something that will be generally accepted in payment-this is the " (15) of exchange" function of money. But there must also be something that can serve as a (16) abode of purchasing power, in which the seller holds the proceeds in the interim (17) the first sale and the (18) purchase, or from which the buyer can (19) the general purchasing power with which to pay (20) what is bought. This is the "asset" function of money. 5（）

A. when
B. before
C. since
D. until