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.

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
sandstone

Category: BROADWAY DEBUTS 
Clue: In 2006, in her first big project since giving birth to twins, she starred on Broadway in "Three Days of Rain"
julia roberts

Category: WEDDINGS 
Clue: This composer was 17, a legal age for men in Mississippi to marry, when he began work on the following:

felix mendelssohn