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: an animal requires air for survival.
Sentence2: The Moon has no atmosphere and no air.

Ex Output:
air

Ex Input:
Sentence1: All lizards are reptiles.
Sentence2: Lizards are tetrapod vertebrates that produce amniotic eggs.

Ex Output:
lizards

Ex Input:
Sentence1: Autumn or Fall is almost over.
Sentence2: when the seasons change from summer to autumn, the amount of daylight will decrease.

Ex Output:
Autumn