The travelers problem.

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Across
  1. 1. what is the busiest airport in the world?
  2. 4. what is country atarted ww2?
  3. 5. what is travel aound the world?
  4. 7. where is the oldest zoo?
Down
  1. 2. a city in northwest Germany near the benelux border
  2. 3. the capital of germany?
  3. 6. what is the cheapest transatlantic flight?