An example of a grad-school level question?
What is the main source of energy for the water cycle?

An example of a grad-school level question?
Which of these explains how a trench can form?

An example of a grad-school level question?
Which of these will best separate a saltwater solution?

An example of a grad-school level question?
A wet towel will dry when it is left in the Sun. Which process occurs to make this happen?