5th geography puzzle

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Across
  1. 3. number of people
  2. 8. river between Nebraska and Iowa
  3. 10. most populated city in Nebraska
  4. 11. a smaller river which flows into a larger one
  5. 13. ocean to the west of California
  6. 14. lines on a map that run north to south
  7. 16. there are seven of these in the world
  8. 17. continent we live in
  9. 19. large pieces of ice
  10. 20. an area of many, many trees
Down
  1. 1. Nebraska is in this region of the USA
  2. 2. largest city in Massachusetts
  3. 4. lines on a map that run east to west
  4. 5. capital city of state of Washington
  5. 6. land surrounded by water on three sides
  6. 7. most populated city in the USA
  7. 9. capital city of Minnesota
  8. 12. mountain range in Colorado
  9. 15. opening in earth in which lava flows out
  10. 18. natural resource used in cars