Given a fact, create a question that can be answered using the fact. Construct the question such that it is unambiguous, has a unique answer and the answer can be given using the fact.

Fact: processes sometimes produce waste products
What product eventually will become human waste?

Fact: some birds are predators
All predators are also carnivorous because predators?

Fact: wind causes erosion

If a thing has been taken from a large object and made much smaller, even minuscule, and this was done over many years, the likely culprit was?