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: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food cold is used to keep food simple and natural as possible.
[A]: cold


[Q]: Sentence1: Babies that are very large or very small at birth are less likely to survive. 
Sentence2: Poor nutrition while in the womb is the major reason why babies are small at birth.
[A]: birth


[Q]: Sentence1: Birds have relatively large brains and a high level of intelligence. 
Sentence2: Birds have relatively large skulls and a high level of intelligence.
[A]:
Birds