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: Refrigerators are major users of electricity. 
Sentence2: Keeping food fresh for a long period of time requires a lot of electricity.
electricity

Sentence1: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.
lightning

Sentence1: Alternation of generation is typical of ferns and Bryophyta. 
Sentence2: ferns have both asexual and sexual reproduction.

ferns