There are three boxes of gold, silver, and copper, and one coin is hidden in one of them. A note is attached to each of the three boxes. The tips above are: (1) the coin is in a gold box; (2) The coin is not in the silver box; (3) The coin is not in the gold box. Only one of these three sentences is true. According to the above conditions, in which box is the coin hidden? ['Coins are in a gold box.', 'Coins in a silver box.', 'Coins in a copper box.', 'No exact answer.']