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.

[Q]: Category: CROSSWORD CLUES "D _ _ _ ER" 
Clue: Macbeth thought he saw one
[A]: a dagger


[Q]: Category: OH "BOY" 
Clue: Slang term for an American infantryman of WWI
[A]: doughboy


[Q]: Category: PLUMBING 
Clue: Doing this to a pipe, unlike doing it to a needle, involves special cutting tools
[A]:
threading