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.

Ex Input:
Sentence1: Batteries are a better source of DC electricity. 
Sentence2: a flashlight requires batteries to produce light.

Ex Output:
Batteries


Ex Input:
Sentence1: Chordates have a complete digestive system and a closed circulatory system. 
Sentence2: All chordates are vertebrates.

Ex Output:
Chordates


Ex Input:
Sentence1: Viruses contain DNA but not much else. 
Sentence2: HIV virus contains RNA.

Ex Output:

Viruses