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: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Yeast and mushrooms are types of fungus.
answer:
mushrooms


question:
Sentence1: pathogens can cause disease. 
Sentence2: pathogens affects the immune system.
answer:
pathogens


question:
Sentence1: Rivers are usually larger than streams. 
Sentence2: Watersheds are creeks, streams and rivers.
answer:

streams