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: riding a bike does not cause pollution. 
Sentence2: riding a bike does not release particles.

A: bike
****
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: Rivers flow in the wilderness. 
Sentence2: A valley is formed by flowing in the wilderness.

A:
flow
****