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: SIGNS & SYMBOLS 
Clue: Symbols of mystery, they're the mysterious doubles of the people who cast them
shadows

Category: LITERATURE 
Clue: Poet who wrote, "Before I built a wall I'd ask to know what I was walling in or walling out"
robert frost

Category: AROUND THE WORLD 
Clue: The Tortola Museum of these British Caribbean islands is in Road Town, the capital

british virgin islands