I Know When I Shop at the Local Grocery Store,I

Multiple Choice

I know when I shop at the local grocery store,I am helping my community.Which economic principle does this statement BEST represent?

A) People usually respond to incentives,exploiting opportunities to make themselves better off.
B) There are gains from trade.
C) One person's spending is another person's income.
D) Overall spending sometimes gets out of line with the economy's productive capacity.