An example of a grad-school level question?
Coal is solid rock that began as organic material that was deposited in a swamp. The formation of coal suggests that

An example of a grad-school level question?
How are green plants an important part of the carbon dioxide-oxygen cycle?

An example of a grad-school level question?
Which of these determines whether a fertilized egg develops into a toad, a snake, or a lizard?

An example of a grad-school level question?
In the 1500s, Nicolaus Copernicus proposed a new theory on the heliocentric structure of the solar system. Which of these statements best describes this new theory?