Why Do Incentives Matter to Economists

Why do incentives matter to economists?

A) People make poor decisions when they're given money they didn't earn.
B) Governments are the source of all incentives and there is value in studying the actions of government.
C) Incentives are often the guiding principle behind greed and exploitation.
D) Incentives explain how people make decisions,and are the key to understanding economics.
E) Without incentives,the distinction between microeconomics and macroeconomics would be unclear.