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: Mutations are essential for evolution to occur. 
Sentence2: Genes are altered for evolution to occur.
[A]: evolution


[Q]: Sentence1: melting is when solids are heated above their melting point. 
Sentence2: Ice is a solid, it's cold and it's hard.
[A]: solids


[Q]: Sentence1: a sandbar is formed by water moving sediment downstream. 
Sentence2: Sandbars are preferred nesting habitat.
[A]:
sandbar