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: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.
groups

Sentence1: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Hydrogen bonds Hydrogen bonds are primarily electrostatic in origin.
Hydrogen

Sentence1: Many of the animals are long-lived, reproducing often but having few young at a time. 
Sentence2: Roundworms create their young sexually.

young