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.
--------
Question: Fact: Pollution is usually harmful to population size of a species. 
Question: What is usually harmful to the population size of a species?

Answer: Pollution.


Question: Fact: glass causes bending of light rays. 
Question: what does glass cause?

Answer: bending light rays.


Question: Fact: Lymphocytes are the key cells involved in an allergy attack. 
Question: Lymphocytes are the key cells involved in what?

Answer:
allergy attack.