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: Batteries are a better source of DC electricity. 
Sentence2: a flashlight requires batteries to produce light.

Answer: Batteries


Question: Sentence1: Most bryophytes are small. 
Sentence2: Most in the same group as mosses are small.

Answer: small


Question: Sentence1: water causes refraction of light. 
Sentence2: Water is a compound of hydrogen and oxygen.

Answer:
water