You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For consistency, answers should be in all lower cased letters.
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Question: Category: MOUNTAINS 
Clue: Cotopaxi, the world's highest active volcano, rises just south of Quito, Ecuador in these mountains

Answer: andes


Question: Category: CURRENT EXPRESSIONS 
Clue: If you're engaging in wishful thinking, you may want to perform this type of "check"

Answer: a reality check


Question: Category: SIZE MATTERS 
Clue: As a rule, the length of this item should be 3 times the thickness of the board being fastened with it

Answer:
nail