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.

[EX Q]: Category: A WALK ACROSS THE CHARLES BRIDGE 
Clue: Originally called Stone Bridge, the Charles Bridge was built with this "stone", like the walls of the White House
[EX A]: sandstone

[EX Q]: Category: 20th CENTURY AUTHORS 
Clue: Ayn Rand once cited this late Mike Hammer author as her favorite popular writer
[EX A]: mickey spillane

[EX Q]: Category: PAUL REVERE 
Clue: In 1775 Congress commissioned Revere to set up a mill to make this product whose main ingredient is saltpeter
[EX A]:
gunpowder