The answer is C sorry if it is wrong
The Precambrian Era was the longest era in the Earth's history. It lasted for approximately 4 billion years!
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13. D
14. C
15. B
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Over the past 50 years, six Nile Basin countries have built 25 hydroelectric dams.
A because Swiden farming requires clearing old crops by burning them and leaving them to regenerate. The burning requires the most soil to be cleared.