In the following passage, the numbered gaps indicate missing words. Against each number in the list below the passage, four options are given in columns lettered A to D. Choose the word that is the most suitable to fill the numbered gaps in the passage.

Money serves as a ....71..... of exchange modern world. This is perhaps the most important 72 of money. People who have money can use it to buy goods and.73......Without it, trade will be carried out on the basis of ...74.... where goods or services are exchanged as was the practice in the years gone by. This mode of trading has a number of disadvantages, as people will have to match their .....75..... With those of other people. For example, if a hunter wants to trade his ....76... for yam, he must find a ..... 77... who needs what he is trading. Another difficulty is determining the ....78..... of each item needed in the exchange. Therefore, this mode of trading is no longer commonly practised. Nowadays, people pay money for goods and services rendered both locally and internationally. International trade boosts the....79...of a nation. The ...80..... frequently used in international trade is the US Dollar.