Given scientific fact as input, generate the question from this fact such that it can be answered from the input.

A student should use a balance to compare the masses of two small rocks.
Which tool should a student use to compare the masses of two small rocks?

Covalent solutes separate into individual molecules when dissolved.
Covalent solutes separate into what when dissolved?

The pupil is the name of the black opening in the eye that lets light enter.
What is the name of the black opening in the eye that lets light enter?