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: cell division often causes growth. 
Sentence2: Cell division leads to reproduction.

A: cell
****
Q: Sentence1: Hail, rain, sleet, and snow are referred to as precipitation . 
Sentence2: Hail that falls on land may soak into the ground, becoming groundwater.

A:
Hail
****