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: Viruses are usually considered to be nonliving.
Sentence2: Viruses are usually acquired from contact with infected animals.

Ex Output:
Viruses

Ex Input:
Sentence1: high mountains with well-rounded peaks can be formed by collision of crustal plates.
Sentence2: high mountains with well-rounded peaks can be formed by collision of plate tectonics.

Ex Output:
collision

Ex Input:
Sentence1: the moon revolving around the Earth causes the phases of the moon.
Sentence2: Phases of the moon, however, depend on the relative positions of the Earth, moon, and Sun.

Ex Output:
Earth