General Knowledge crossword puzzle

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Across
  1. 5. The process by which plants make food. (8)
  2. 7. The chemical symbol for water. (2)
  3. 9. The number of continents on Earth. (7)
  4. 11. The force that pulls objects towards the center of the Earth. (6)
  5. 12. The smallest planet in our solar system.
  6. 13. The capital city of France
  7. 15. The chemical symbol for gold
  8. 16. The longest river in the world.
  9. 17. The world's tallest mountain. (6)
Down
  1. 1. The first man to walk on the moon.
  2. 2. The capital city of Australia. (8)
  3. 3. The study of stars and planets
  4. 4. The largest planet in our solar system.
  5. 6. The author of "Romeo and Juliet".
  6. 8. The largest mammal
  7. 10. The largest ocean on Earth. (7)
  8. 14. The main organ for breathing in humans. (5)