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: being burried under soil and mud changes peat into coal through extreme heat and pressure in a swamp over a long period of time. 
Sentence2: Marble is used for sculptures, and coal is used for fuel and energy like light.
coal

Sentence1: a rainbow is formed by refraction of light by separating light into all different colors. 
Sentence2: Rainbows form when raindrops refract sunlight.
refraction

Sentence1: Sweat glands pump perspiration through pores. 
Sentence2: Perspiration comes through pores and is evaporated by energy from body heat.

perspiration

