青藏高原上的主要农作物有：（   ）

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    On a snowy and windy afternoon, Ann, a ten-year-old girl, went out to play. She was walking along the sands when she was blown into a ditch (壕沟) by the seashore. She was frightened and tried her best to climb out. But the ditch was too deep and she was too weak to get out of it. So Ann cried at the top of her voice for help. But what she could hear over the snow ditch was nothing but the terrible noise of the wind. Nobody came to her and nobody knew where she was. She struggled again and again. Her face was struck by the strong wind, snow and sand, and was almost frozen. Her hands were stiff. She also felt that she was worn out. She started to cry hopelessly. Just at the moment Ann saw a black dog appearing through the heavy snow. It was Victor, her true friend. He was glad to see the sign of life. And the dog set out to work as soon as he got to Ann. He cleaned away the snow around her with his own paws and hind legs, and then reached out his big strong fur head to Ann. The little girl closed her arms round Victor's neck. The dog backed away slowly, pulling her out of the ditch little by little.

    Successfully, Ann got out of the ditch at last. Then she struggled to her feet. With great difficulty, led by her true friend Victor, she was rescued. Victor, the black dog, was given a gold medal and was honoured as Brave Hero Dog of America.

俄罗斯的最大城市是（　　）