An example of a grad-school level question?
Rocks are classified as igneous, metamorphic, or sedimentary according to

An example of a grad-school level question?
Living things depend on energy from

An example of a grad-school level question?
Timber companies can best manage the number of trees in forests by

An example of a grad-school level question?
A student drops a ball. Which force causes the ball to fall to the ground?