Henry's General Knowledge Puzzle

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Across
  1. 1. , the capital of bulgaria
  2. 3. , was a prime minister for 49 days
  3. 6. , it is the strongest muscle in your body
  4. 8. , record holder for the 50m breastroke.
  5. 9. , the inventor of the lightbulb
  6. 10. , how many states are there in the USA.
Down
  1. 2. , the inventor of the telephone
  2. 4. , who created E = MC squared
  3. 5. , the tallest volcano
  4. 7. , you would use it when drawing a straight line