An example of a grad-school level question?
Which is the most likely reason why scientific theories change?

An example of a grad-school level question?
Which mineral has six-sided transparent crystals that will scratch glass?

An example of a grad-school level question?
What would best regulate the temperature of an overheated body?

An example of a grad-school level question?
Plankton are tiny ocean organisms. The role of one type of plankton is to use the energy from the Sun to produce food that other animals eat. Which organism has the same role in the ocean as this type of plankton?