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: Mad Cow disease is a concern. 
Sentence2: pathogens can cause Mad Cow.

Answer: Cow


Question: Sentence1: Viruses contain DNA but not much else. 
Sentence2: viruses contain encoded information but not much else.

Answer: Viruses


Question: Sentence1: Echinoderms lack a centralized nervous system. 
Sentence2: Starfish lack a centralized nervous system.

Answer:
a