How have roman roads impacted our modern society

People keep spending additional units of a particular resource on a want until their marginal benefit is  decreasing withgreater thanless thannot affected by  their marginal cost.

What is a small water source like a stream or brook?

Can someone me choose a broad topic and area of focus i am really doing this as a tally to see which one most people pick ok water pollution global warming endangered species atmosphere for the !