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.

[EX Q]: Sentence1: Viruses are parasites of cells. 
Sentence2: Populations of viruses do not grow through division because they are parasites.
[EX A]: are

[EX Q]: Sentence1: Instead, the body is covered with a protective shell of bony armor. 
Sentence2: Most mollusks have protective of bony armor.
[EX A]: armor

[EX Q]: Sentence1: Many practical devices, such as the mercury thermometer, work on the principle of thermal expansion. 
Sentence2: Thermal expansion is used to measure temperature.
[EX A]:
expansion