Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

[Q]: Sentence1: DNA is made up of nucleotides. 
Sentence2: Mutations can change the structure of DNA.
[A]: DNA


[Q]: Sentence1: burning fossil fuels increases the carbon in the atmosphere. 
Sentence2: the byproduct of fossil fuels is carbon.
[A]: carbon


[Q]: Sentence1: Hairs stand on end, the heart races and fight or flight hormones flood the body. 
Sentence2: threatening behavior causes the heart to race and hormones to flood the body.
[A]:
body