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: Antigens are proteins foreign to the body. 
Sentence2: antigens are proteins.

Answer: proteins


Question: Sentence1: Some trees are maples. 
Sentence2: planting maples has a positive impact on an ecosystem.

Answer: maples


Question: Sentence1: Toads and frogs are both amphibians. 
Sentence2: Toads have a relatively complex circulatory system with a three chambered heart.

Answer:
Toads