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: June Summer Triangle Three bright stars light up the summer sky. 
Sentence2: Nuclear reactions in stars cause them to brighten up the summer sky.

Answer: bright


Question: Sentence1: Mitosis is cell division. 
Sentence2: mitosis often causes growth.

Answer: Mitosis


Question: Sentence1: Fertilization of gametes produces a diploid zygote. 
Sentence2: Female gametes are called eggs.

Answer:
gametes