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.

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

A: bending
****
Q: Sentence1: Nonmetal elements are far fewer in number. 
Sentence2: There are 17 nonmetals on the periodic table.

A: Nonmetal
****
Q: Sentence1: Some mountains are caused by erosion. 
Sentence2: some mountains are caused by wind and rain.

A:
mountains
****