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: Gravity is a force that pulls on things. 
Sentence2: A force that pulls on things pulls objects towards planets.

A: force
****
Q: Sentence1: An accounting period is simply a period of time. 
Sentence2: seconds are used to measure a period.

A: period
****
Q: Sentence1: Condensations is a warming process. 
Sentence2: Clouds form from a warming process.

A:
process
****