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: Parasites are organisms that live off a host. 
Sentence2: roundworms may be free-living or live off a host.

Answer: host


Question: Sentence1: Some mollusks are nearly microscopic. 
Sentence2: Some squids are nearly microscopic.

Answer: Some


Question: Sentence1: Carbon dioxide is the primary greenhouse gas. 
Sentence2: greenhouse gas concentrations in the air have increased over the last decade dramatically.

Answer:
gas