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: air pollution can cause the pH of soil to decrease. 
Sentence2: Acidity is measured with a pH meter or with pH paper strips.

A: pH
****
Q: Sentence1: All monkeys are mammals. 
Sentence2: monkeys conserve body heat with their hair or fur.

A: monkeys
****
Q: Sentence1: Playing is one way mammals and other animals learn how to behave. 
Sentence2: Playing is one way sea lions learn how to behave.

A:
Playing
****