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.

[Q]: Sentence1: Light source is an ultra-bright, unbreakable LED Bulb. 
Sentence2: LEDs convert electricity into light and heat energy.
[A]: LED


[Q]: Sentence1: Combustion generates toxic fumes. 
Sentence2: High temperatures can cause toxic fumes.
[A]: fumes


[Q]: Sentence1: Vertebrate chordates have a backbone. 
Sentence2: Birds are a class of the chordates or vertebrate phylum.
[A]:
Vertebrate