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


[Q]: Sentence1: Cows are social animals. 
Sentence2: when a cow moves, chemical energy is converted to mechanical energy.
[A]: Cows


[Q]: Sentence1: Trees are the largest of living things. 
Sentence2: trees require energy for survival.
[A]:
Trees