Given a category and a set of five words, find the word from the set that does not belong (i.e. is the least relevant) with the other words in the category. Words are separated by commas.
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Question: Category: elements 
Words: ice, air, fire, hire, combustion

Answer: hire


Question: Category: physical activity 
Words: drop, fall, leaves, bend, exercise

Answer: leaves


Question: Category: type of rigidity 
Words: corporation, firm, rough, resistant, stiff

Answer:
corporation