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2. Source: Helena Grigar

4. Photo by Tony Linck - Getty Images

5. Image by Emilia Karbownik Image by Caroline Paré

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7. Image by David W. Carmichael

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11. 6.0

12. Image by David W. Carmicheael

13. -3 -2 -1 0 +1 +2 +3

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15. Image by Free Software Foundation

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17. Imag e by David W. C armichael

18. Image by David W. Carmichael

20. Thank you!