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: Mating is generally preceded by courtship. 
Sentence2: Mating is generally similar across species.

Answer: Mating


Question: Sentence1: Trees have woody stems covered with bark. 
Sentence2: Evergreens have woody stems covered with bark.

Answer: bark


Question: Sentence1: Antibodies are produced to fight antigens. 
Sentence2: plasma cells secrete antigen fighters.

Answer:
antigens