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: a solution is formed by one substance being dissolved in another substance. 
Sentence2: A solution is formed when limestone is dissolved in ocean water.
[EX A]: formed

[EX Q]: Sentence1: Echinoderms lack respiratory and excretory systems. 
Sentence2: echinoids lack a respiratory system.
[EX A]: respiratory

[EX Q]: Sentence1: the movement of tectonic plates causes volcanic eruptions. 
Sentence2: earthquakes are caused by tectonic plates.
[EX A]:
plates