The field of study of economy as a sub-discipline of social sciences is based on some suppositions. The first hypothesis is that the sources are limited. The second is based on an assumption that human needs are infinite. The third presumes that people act rationally while they fulfill their needs on choice and preferance. Scarcity and choice are the two main concepts of the economics discipline. The analysis unit of economy is market. It only analyses the relations of economical providence, actions and production, circulation, distribution and consumption for two actors. To put it differently, actors of economic activity are the producer (firm) and the consumer (household). The correct answer is C.