Answer:
Currency
Economics
Step-by-step explanation:
"Currency is a medium of exchange for goods and services"(investopedia). So we exchange currency for goods and services within a give locality or country. It is the generally accepted medium of exchange in a country or "a system of money in general use in a particular country"(Oxford dictionary).
Economics comes into play because human needs and wants are endless. Hence, there is need to prioritize them using a scale of preference in which there must be alternatives forgone. This is the main thrust of the study of economics.