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.

Sentence1: Acid rain is precipitation which pH is 5.7 or lower. 
Sentence2: gases from burning coal causes precipitation which pH is 5.7 or lower.
5

Sentence1: Heat and temperature are the same. 
Sentence2: a thermometer is used to measure heat.
Heat

Sentence1: For example, beef is a functional food. 
Sentence2: beef has organic molecules that store energy in their chemical bonds.

beef