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


[Q]: Sentence1: Finally, the fluid in the nephron reaches a collecting duct . 
Sentence2: fluid in the kidneys collect into ducts.
[A]: fluid


[Q]: Sentence1: Viviparous species include the hammerhead, bull shark, blue shark and lemon sharks. 
Sentence2: hammerhead, bull shark, blue shark, and lemon sharks are called therian mammals.
[A]:
blue