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

Sentence1: Endospores are commonly found in soil and water. 
Sentence2: Some bacteria form resistant cells called endospores.
Endospores

Sentence1: Plants detect and respond to the daily cycle of light and darkness. 
Sentence2: Plants detect and respond to diurnal cycles.

Plants