Use the graph below to answer the following question: A line graph depicting the approximate growth of the population in Europe from 1750 through 2000. The y-axis of the graph starts at zero and goes to 800 million, using an interval of 100 million. The graph shows the population of Europe was approximately 150 million in 1750, 200 million by 1800, 275 million by 1850, 400 million by 1900, 550 million by 1950, and 725 million by 2000.
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Which of the following reasons is the best possible explanation for the changes in Europe's population since 1750?

An increase in scientific and medical discoveries improved life expectancies.
Political revolutions caused a shift from absolute to constitutional monarchies.
The Enlightenment encouraged European peasants to increase their family sizes.
The Scientific Revolution led to a sharp increase in immigration.