general knowledge

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Across
  1. 1. Largest moon of Saturn
  2. 3. Input device for typing
  3. 4. Formerly classified as the ninth planet
  4. 5. Planet with prominent rings
  5. 8. Essential gas for breathing
  6. 10. Second planet from the sun
Down
  1. 2. Mythical lost city
  2. 6. Natural light display in polar regions
  3. 7. Longest river in the world
  4. 9. Historic fortification in China