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: Specialization occurs when competing species evolve different adaptations.
Sentence2: evolving different adaptations increases survival.

Ex Output:
adaptations

Ex Input:
Sentence1: microscope is used to see small things by biologists by making them appear bigger.
Sentence2: Something invented by Leeuwenhoek is used to see small things by biologists by making them appear bigger.

Ex Output:
appear

Ex Input:
Sentence1: Running water is better able to dissolve oxygen and nutrients than standing water.
Sentence2: Oxygen and nutrients dissolve easily in rivers.

Ex Output:
dissolve