TASK DEFINITION: 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.
PROBLEM: Category: HE WAS IN THAT? 
Clue: As a child Robert Blake played a Mexican boy in this Bogart classic directed by John Huston

SOLUTION: "the treasure of the sierra madre"

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

SOLUTION: sic

PROBLEM: Category: HOW DOES YOUR GARDEN GROW? 
Clue: By its derivation the only thing in an arboretum should be these, no shrubs or other plants

SOLUTION:
trees