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 Q]: Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: Allergens can trigger asthma attacks.
[EX A]: allergen

[EX Q]: Sentence1: Cells are the units of function in living things. 
Sentence2: living things cannot survive without oxygen.
[EX A]: living

[EX Q]: Sentence1: conserving water can be used for survival in a dry environment. 
Sentence2: Conserving water can help humans survive.
[EX A]:
conserving