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: drought is when amount of precipitation decreases. 
Sentence2: Drought decreases the availability and abundance of the natural food supply.

A: drought
****
Q: Sentence1: mountains are formed by earthquakes. 
Sentence2: Mountains are formed by moving plates.

A: are
****
Q: Sentence1: Gills are used for respiration. 
Sentence2: the thing that gills are used for begins with ventilation.

A:
Gills
****