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.

[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
[A]: sandstone


[Q]: Category: WHAT SHOULD I "DU"? 
Clue: A philosophical system that seeks to explain all phenomena in terms of 2 distinct principles
[A]: dualism


[Q]: Category: POETIC LICENSE 
Clue: The 2001 biography "Savage Beauty" details the lustful life of this "What Lips My Lips Have Kissed" poet
[A]:
edna st. vincent millay