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: HEAVY MACHINERY 
Clue: By definition it's a machine that gives a surface an even degree of slope

SOLUTION: grader

PROBLEM: Category: PLAYBILL 
Clue: This musical's "American Dream" ended on B'way after 4,097 performances--& a lot of helicopter flights

SOLUTION: miss saigon

PROBLEM: Category: WHERE IT AILS YOU 
Clue: Tinnitus

SOLUTION:
the ear