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: Many plants respond to the days growing shorter in the fall by going dormant. 
Sentence2: Many plants respond to the autumnal equinox by going dormant.
[A]: Many


[Q]: Sentence1: a polar bear requires a cold environment. 
Sentence2: polar bears live where there are fewer animals.
[A]: bear


[Q]: Sentence1: Lung cancer is most often caused by exposure to tobacco smoke. 
Sentence2: exposure to tobacco smoke causes tumors.
[A]:
smoke