Las Colonias" refers to settlements

a. that are often called "America's Third World."
b. in poor areas of Mexico, close to the Texas border.
c. containing Hispanic Americans, almost all of whom are illegal immigrants.
d. outside of major cities.

Air pollution: “combustion results in gases such as nitrogen oxides, nitrogen dioxide and particulates. the main causes of air pollution include transport, domestic combustion and industrial processes. pollutants from these sources can cause problems in the immediate vicinity and a distance away.”

I  cant see the question.