Mr Evans works in Sydney. Last week he had a two-week holiday, but he didn't know where to go. He said to his friend Robert, "I hate the hot weather here, but I can't think of a cool place in Australia. Where shall I take my holiday?" "That's easy," said Robert, "You can go to Moscow. Snow and ice are covering the ground there now." Mr Evans agreed with his friend. He bought a plane ticket and soon arrived in Moscow. He was having a good time there, but one day he got into trouble . After lunch, he went to a park outside the city. He noticed a dog following him when he was walking past a house. It was hungry and wanted some food to eat. But Mr Evans had no food in his pockets. He tried to shoo   it away, but it began to bark at him. Just at that moment, he saw a stone on the ground. He tried to pick it up, but he couldn't. "How strange these Russians are!" Mr Evans said to himself, "They do not tie up   their dogs, but firmly tie down the stones!" Mr Evans couldn't pick up the stone because  _  .
it was too cold it was too heavy the Russians tied their stones to the ground it was not a stone