Which of the following is not a type of air pollution?

a.) acid rain

b.) mercury

c.) ozone

d.) oxygen

Which evidence is most likely used to indicate the beginning of solar system formation? a. materials combined to form a mass. b. materials were pulled together by gravity. c. water condensed and collected to form oceans. d. different species of microorganisms lived on earth.

Sink holes may eventually for to join a. wide valleys b. zone of aeration c. dripstones d. aquifer

Where the main factor that enabled the growth of cities and civilizations was the existence of