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

SOLUTION: bear

PROBLEM: Sentence1: a flashlight converts chemical energy into light energy. 
Sentence2: Chemical energy converted to light energy requires batteries.

SOLUTION: chemical

PROBLEM: Sentence1: Polyps usually reproduce asexually. 
Sentence2: Polyps are benign growths in the colon.

SOLUTION:
Polyps