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.

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

Sentence1: Asbestos is a dangerous carcinogen. 
Sentence2: Asbestos causes cancer.
Asbestos

Sentence1: Fall starts in September and is windy and dry. 
Sentence2: many plants respond to the days growing shorter in September by going dormant.

September