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


question:
Sentence1: Many birds perform elaborate courtship dances. 
Sentence2: Many birds perform dances before they mate.
answer:
Many


question:
Sentence1: Birds fly using wings. 
Sentence2: birds use muscles for flight.
answer:

Birds