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: Some trees are maples. 
Sentence2: planting maples has a positive impact on an ecosystem.
maples

Sentence1: Refraction is the bending of light. 
Sentence2: a rainbow is formed by bending of light by separating light into all different colors.
bending

Sentence1: smoking causes direct damage to the lungs. 
Sentence2: Smoking causes direct damage to the air sacs.

damage