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

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


[Q]: Population is an important level of organization in ecology and the unit of microevolution.
[A]: What is an important level of organization in ecology and the unit of microevolution?


[Q]: The photic zone extends 200 meters deep.
[A]:
How many meters deep does the photic zone extend?