ie or ei?

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Across
  1. 2. A synonym for this word is 'robber'.
  2. 4. A written acknowledgement that you have purchased something.
  3. 6. Light grey with a brownish tinge.
  4. 8. Free from the demands of works or duty (e.g. "She is a lady of _______.")
  5. 9. He studied hard and ________ the result he was hoping for.
  6. 12. An ancient Egyptian script which uses pictures.
  7. 14. Physics, biology and chemistry and all strands of _______ .
  8. 15. A person who lives near another.
  9. 16. To recognise, observe or understand.
  10. 18. To have faith or consider true.
  11. 19. From another country or nation.
Down
  1. 1. She measured her ______ and discovered that she was 154cm tall.
  2. 3. This word is a homophone and means 'part of' or 'segment'.
  3. 5. The legal age you can vote in Australia.
  4. 7. To trick or cheat.
  5. 10. Having an excessively high opinion of oneself.
  6. 11. The amount of heaviness or mass.
  7. 13. A short duration.
  8. 15. Not one or the other.
  9. 17. The overhead interior surface of a room.