Opposites attract

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Across
  1. 2. Imitation
  2. 6. Separate
  3. 7. Straight
  4. 8. Artificial
  5. 10. Large
  6. 11. Dirty
  7. 12. Smooth
  8. 14. Serious
Down
  1. 1. Break
  2. 2. Below
  3. 3. Fail
  4. 4. Knowledge
  5. 5. Heavy
  6. 9. Useful
  7. 11. Expensive
  8. 13. Sell