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: a fire requires oxygen to burn. 
Sentence2: A fire requires something with exactly eight protons to burn.

A: burn
****
Q: Sentence1: the Earth being tilted on its rotating axis causes seasons. 
Sentence2: the planet's orbit and tilt causes seasons.

A: seasons
****
Q: Sentence1: Soil erosion harms farm and grazing lands and increases flooding and desertification. 
Sentence2: When a river floods, that river harms farm and grazing lands.

A:
farm
****