Final answer:
A person's behavior in market interactions relates to the study of economics, which encompasses both individual choices and broader market forces of demand and supply.
Step-by-step explanation:
The behavior a person exhibits when they interact with people in the market is best described by option d. economics. This is because economics involves studying how individuals and groups make choices regarding the allocation of resources and how these choices influence production, distribution, and consumption of goods and services within a market.
A market economy is characterized by such interactions where decisions are made based on individual choices and the forces of demand and supply. In essence, economics encompasses the micro and macro-level decisions and interactions that occur in a market economy, including the actions of specific agents like households, workers, and business firms, which is the focus of microeconomics.