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: Passive immunity lasts only as long as the antibodies survive in body fluids. 
Sentence2: A pregnant woman will pass antibodies to the fetus.

Ex Output:
antibodies


Ex Input:
Sentence1: a fire requires oxygen to burn. 
Sentence2: Oxygen has  eight protons and eight electrons.

Ex Output:
oxygen


Ex Input:
Sentence1: Results underline the benefits of such vaccination policy. 
Sentence2: vaccination policies have benefits to immunity.

Ex Output:

benefits