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: DR. WHO... 
Clue: specializes in X-rays & elements, like the one with the atomic number 88 for treating diseases

Answer: a radiologist


Question: Category: AMERICAN POETRY 
Clue: In "Stopping by Woods on a Snowy Evening", he wrote that he had "promises to keep, and miles to go before I sleep"

Answer: frost


Question: Category: CLASSICAL MUSIC 
Clue: The music of this country's national anthem is attributed to a native son, Mozart

Answer:
austria