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: FOLKLORE
Clue: Old Stormalong soaped his ship to squeeze through the English channel; the soap rubbed off on these cliffs
[A]: the cliffs of dover

[Q]: Category: DARWIN
Clue: Darwin's paternal grandfather, Erasmus Darwin, declined an offer to become private physician to this 18th C. king
[A]:
george iii