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.
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Question: Category: U.S. GEOGRAPHY 
Clue: The West Point Military Reservation includes Constitution Island, which lies in this river

Answer: the hudson river


Question: 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

Answer: sandstone


Question: Category: HISTORIC NAMES 
Clue: In 1930 he led a march to the sea to collect salt to protest a monopoly by the government of India

Answer:
mahatma gandhi