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.

[EX Q]: Sentence1: Heterotrophs are living things that cannot make their own food. 
Sentence2: food contains organic molecules.
[EX A]: food

[EX Q]: Sentence1: a fire requires oxygen to burn. 
Sentence2: If the oxygen is removed, the fire is smothered.
[EX A]: oxygen

[EX Q]: Sentence1: clouds are formed by water vapor rising into colder regions of the atmosphere and condensing. 
Sentence2: Cloud cover and precipitation  cause temperature fluctuations.
[EX A]:
clouds