The correct answer is - C. 1975 - 1999.
The period between 1975 and 1999 was a period in which the world population grew for around 2 billion people. Even thought that is the same rise as in the period between 1930 and 1975, still this period is shorter, and is just 24 years the world population grew from approximately 4 billion people to approximately 6 billion people.
