Final answer:
What you can afford is primarily limited by money, which is directly related to the concept of a budget constraint in economics. While other factors like preferences and demand influence choices, only money directly restricts purchasing power.
Step-by-step explanation:
The question pertains to the concept of budget constraints and what limits an individual's ability to afford goods and services. When presented with the options A. substitutes, B. money, C. externalities, D. demand, E. preferences, the correct answer is B. money.
The concept of budget constraint plays a crucial role in economics because it represents the range of choices available based on one's financial resources. Since one cannot have everything they want due to the scarcity of resources, they must make choices within their economic behavior. Your capacity to purchase is directly tied to the amount of money you have, as this determines the feasible options within your budget constraint. Preferences, substitutes, demand, and externalities can influence choices, but they do not directly limit what you can afford like money does.
For the additional question regarding a price ceiling, the correct answer is D. neither. A price ceiling does not shift the demand or supply curve but rather imposes a restriction on how high the price of a good can go.