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: I'M JUST RUNNING IN FOR... 
Clue: ...20 first-class stamps, which will now cost this much total

Answer: $7.40


Question: Category: SUN 
Clue: In the main reaction making the sun's energy, 2 of these nuclear particles fuse & one becomes a neutron

Answer: protons


Question: Category: WE DON'T NEED NO STINKIN' BADGERS! 
Clue: Badgers belong to this family, Mustelidae, but you probably have never sung "Pop Goes The Badger"

Answer:
weasel