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.

Input: Consider Input: Fact: if copper is exposed to a source of heat then that copper may easily become hot. 
Question: What can easily become hot if exposed to heat?

Output: copper.


Input: Consider Input: Fact: A bicycle is a vehicle that requires smooth surfaces. 
Question: What kind of surface does a bicycle require to ride on?

Output: smooth.


Input: Consider Input: Fact: kidneys make up the excretory system. 
Question: Kidneys are a part of what system?


Output: excretory.