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.

[EX Q]: Fact: Ejaculation of sperm can be inhibited by bacterial infection. 
Question: Bacterial infection can inhibit ejaculation of what?
[EX A]: sperm.

[EX Q]: Fact: Melanin amount is a polygenic trait. 
Question: what is a polygenic trait?
[EX A]: melanin amount.

[EX Q]: Fact: rivers are usually larger than small water crossings. 
Question: what are usually larger than small water crossings?
[EX A]:
rivers.