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.

Category: ANIMALS IN LITERATURE 
Clue: This knight errant's steed in Rocinante, a draft horse originally belonging to his neighbor
don quixote

Category: JOE THE PLUMBER 
Clue: Joe knows how to "assemble" 2 words into this 1-word toilet part by combining comedienne Lucille & a male chicken
a ballcock

Category: U.S.A. 
Clue: It was first surveyed to settle a dispute between the Penn family & the Calvert family

mason-dixon line