Whats caused by natural sources, such as dust and smoke, and human sources, such as gas powered cars and trucks?

Natural sources are probably those coming from pollution. One example is the smoke and ash rain created by volcanic eruptions. Human sources are those made from humans (of course). One example is acid rain which is a result of different chemicals evaporated into atmosphere.

Air pollution.

Explanation:

Air pollution can be caused by natural and human created sources, like gas powered cars and trucks, and dust and smoke, air pollution affects most of the individuals in the world, since most of us need oxygen to breathe and to exist, so air pollution in cities creates allergies and respiratory system diseases.

answer(c) carved on a babylonian clay tablet that showed earth as a flat circular disk;