Write a correct answer to the given question based on its associated fact. Make sure that your answer is contained in the associated fact. Don't be creative and introduce any new word that is not mentioned in the associated fact! Remember that the associated fact has been rearranged to form the question. So, the correct answer words must lie within the associated fact. The correct answer can be a word, phrase, or even a sentence.

Fact: When a population suddenly gets much smaller the effects are unpredictable. 
Question: What is the effect of a population suddenly getting much smaller?
it is unpredicatbale.

Fact: Humans have collected and grown fungi for food for thousands of years. 
Question: What have humans collected and grown as food for thousands of years?
fungi.

Fact: A compound which can donate a proton from burning coal and oil dissolving in water in the atmosphere causes a compound which can donate a proton rain. 
Question: What comes from burning coal and oil dissolving in water in the atmosphere?

A compound that donates proton.