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: Hair helps to insulate and protect the body. 
Sentence2: most mammals have insulation that also protects the body.

A: body
****
Q: Sentence1: Macroevolution is more than repeated rounds of microevolution. 
Sentence2: evolution over geologic time above the level of the species is more than repeated rounds of microevolution.

A: microevolution
****
Q: Sentence1: Coal-fired power stations can cause acid rain and contribute to global warming. 
Sentence2: Certain types of electricity production can cause acid rain and contribute to global warming.

A:
acid
****