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.
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Question: Sentence1: Some birds are pollinators that co-evolved with plants. 
Sentence2: insects pollinate plants.

Answer: plants


Question: Sentence1: Organisms cluster around hydrothermal vents in the ocean floor. 
Sentence2: vents on the ocean floor are powered by heat.

Answer: vents


Question: Sentence1: energy is used for heating a building by a heating system. 
Sentence2: Architects create structures that use energy for heating.

Answer:
energy