It is believed that it took about 800 thousand to 1 million years for the earth's population to reach the 250 million total which existed at the end of the first century AD. For some time after that, disease, famine  and war kept the population increase down to a rate of 1 percent a year so that more than 15 centuries passed before the population reached 500 million. But in the next 250 years, up to 1850, the population of the world shot to 1 billion and today it has reached 3.5 billion. Scientists say that in the next 35 years the population of the world will double, reaching almost 7 billion by the year 2010. When experts are asked what are the most effective measures that can stop over population, they reply that at least three measures can be considered. (A) Increasing sources and supply of food for under-developed countries. (B) Increasing the industrialization of under- developed countries. (C) Controlling birth. The experts add, however, that none of the above measures can be effective by itself, and that all must be combined into one whole program. They also agree that without controlling of births, any other measures are doomed   to failure. The population of the world doubled between the year   _  .
1850 and today 100 and the year 1400 100 and the year 1600 1 and the year 100