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: lightning ignites fires. 
Question: what can lightning ignite?

Answer: fires.


Question: 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?

Answer: copper.


Question: Fact: the Earth being tilted on its rotating axis causes summer. 
Question: What does the Earth being tilted on its rotating axis cause?

Answer:
summer.