'y' as in pyramid

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Across
  1. 4. A butterfly has a vertical line of __________ as both wings are identical of each other.
  2. 5. The ancient Egyptians built these as a tomb
  3. 6. A 3D object that has 3 faces
  4. 8. A colourless fluid in the body containing white blood cells
  5. 9. A lot of songs today have explicit ___________ in them.
  6. 12. This typically involves exercises on bars, beam, floor, and vaulting horse
  7. 16. To supply or inject something with oxygen.
  8. 17. 21% of the air we breathe is this gas
Down
  1. 1. a person or event that quickly causes change or action
  2. 2. A meaning that is mysterious or obscure
  3. 3. To feel sorry for someone
  4. 7. It was a __________ Tuesday morning at school when we had our PE lesson.
  5. 10. The capital city of this country is Cairo.
  6. 11. two or more words having the same spelling or pronunciation but different meanings
  7. 13. In Greek __________, Zeus was the ruler of Gods and men
  8. 14. An emoji is an example of a _____________ used instead of words
  9. 15. Happy, glad, cheerful & joyful are all examples of a ____________ for the word 'delighted'.