Answer: c) 1.65 billion
In March of 2008 the world human population reached 6.60 billion, however in 1900 there were only 1.65 billion people on the planet. The population has continued to grow "at rates that were unprecedented before the 20th century, although the rate of increase has almost halved since its peak, which was reached in 1963, of 2.2 percent per year. The world's population, on its current growth trajectory, is expected to reach nearly 9 billion by the year 2050."
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