Final answer:
The economics of agglomeration makes it essential for the "bottom billion" to develop.
Step-by-step explanation:
The economics of agglomeration makes it c) essential for the "bottom billion" to develop. Agglomeration refers to the concentration of economic activities in specific regions or cities, which leads to various advantages such as economies of scale, better infrastructure, access to a skilled workforce, and innovation. These factors are crucial for the development of countries with limited resources and opportunities, as they enable them to attract investments, create jobs, and improve their overall economic performance.