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: Chromosomes are the form of the genetic material of a cell during cell division. 
Sentence2: Microtubules move the genetic material of a cell during cell division.

Ex Output:
cell


Ex Input:
Sentence1: An astronaut is a scientist who is a space explorer. 
Sentence2: Space explorers require preserved food for long flights.

Ex Output:
explorer


Ex Input:
Sentence1: Prokaryotes are single-celled organisms that lack a nucleus. 
Sentence2: Bacteria and archaebacteria are single-celled organisms that lack a nucleus.

Ex Output:

lack