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: Any antigen that causes an allergy is called an allergen. 
Sentence2: molds are antigens.
answer:
antigen


question:
Sentence1: Finally, the fluid in the nephron reaches a collecting duct . 
Sentence2: fluid in the kidneys collect into ducts.
answer:
fluid


question:
Sentence1: bacteria in soil convert atmospheric nitrogen into a form usable by plants. 
Sentence2: Plants have to have nitrogen to grow.
answer:

nitrogen