Exit which of the following is not a source of earth's internal heat?
a. mantle convection
b. radioactive substances
c. gravitational contraction
d. past bombardment by asteroids

Which of the following is a way that advancements in technology improve humans' ability to measure air quality and protect human health?

Acharreadas is a popular mexican thing where people display varying skills of horsemanship much like what events in the united states?

The oil and gas found in the middle east are regulated by a. organization of petroleum exporting countries b. southwestern asian oil refineries c. north atlantic treaty organization