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: intense heat has a negative impact on an organism. 
Sentence2: intense heat has a negative impact on plants.

Ex Output:
heat


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: a plant requires sunlight for photosynthesis. 
Sentence2: They make their own food through photosynthesis.

Ex Output:

photosynthesis