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: DECEMBER 1st
Clue: 1959: 12 countries including the U.S. & the U.S.S.R. sign a treaty to keep this continent a scientific preserve

Answer: antarctica

Question: Category: A CAST OF THOUSANDS
Clue: It's what you're trying to catch when you're fly-casting

Answer: fish

Question: Category: BRIDGES
Clue: This Colorado canyon has the world's highest suspension bridge 1,053' above the Arkansas River

Answer:
royal gorge