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: an animal requires warmth for survival. 
Sentence2: Light and heat and warmth are basic necessities for survival.
[EX A]: warmth

[EX Q]: Sentence1: microbial fuel cells convert chemical energy into electrical energy. 
Sentence2: microbial fuel cells convert chemical energy into kinetic energy.
[EX A]: cells

[EX Q]: Sentence1: Because reptiles are vertebrates, they are chordates. 
Sentence2: Reptiles have backbones.
[EX A]:
reptiles