Correct Answer: (b) 100 years
Note: According to Donella H. Meadows, one of the authors of the book 'Limits to growth', published in the year 1972, if the present trends in world population, industrialization, pollution, food production and resource depletion continue unchanged, there will be a limit to growth in the next 100 years, which will increase the risk of hunger, economic and social risks. In 2004, this limit was reduced to 30 years by Meadows.