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 simplicity, answers should be in all lower cased letters.
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Question: Category: U.S. RIVERS 
Clue: The Falls of Saint Anthony stop this mighty river from being navigable north of St. Paul, Minnesota

Answer: the mississippi


Question: Category: ENGLISH USAGE 
Clue: Latin for "thus", this 3-letter word is put in brackets to indicate an error in a quote

Answer: sic


Question: Category: BALLET 
Clue: Prince Ivan falls in love with an enchanted Tsarevna in Stravinsky's ballet about this magical bird

Answer:
"the firebird"