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: Coral reefs are made up of the accumulated exoskeletons of the coral polyp. 
Sentence2: coral polyps form reefs.
[A]: polyp


[Q]: Sentence1: a thermometer is used to measure temperature. 
Sentence2: a thermometer is used to measure heat.
[A]: a


[Q]: Sentence1: Cellular respiration in cells is necessary for other activities of the body to function properly. 
Sentence2: Converting oxygen and carbohydrates to carbon dioxide and energy is necessary for the body to function properly.
[A]:
body