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 plant requires sunlight to grow. 
Sentence2: Grass needs air and sunlight.
sunlight

Sentence1: All frogs are amphibians. 
Sentence2: frogs have permeable skin that easily absorbs substances from the environment.
frogs

Sentence1: a human requires sleep to be healthy. 
Sentence2: a human is required to dream to be healthy.

healthy