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: Protozoa make humans sick when they become human parasites. 
Sentence2: paramecium are single celled animals that make humans sick when they become human parasites.
become

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

Sentence1: Sunglasses help protect the eyes from glare off the river surfaces. 
Sentence2: Sunglasses can protect against looking at bright objects, like glare off the river surfaces.

Sunglasses