The correct answer is C) Global population increased due to sanitation, medicines, and food production.
The specifics that brought the global population increase from 1.8 billion to 2.5 billion between 1913 and 1950 was that global population increased due to sanitation, medicines, and food production.
Population on Earth increased during the time frame of 1913 to 1950 due to three aspects. The first one, sanitation. Public health, sewing services, clear water services were much better than in previous years. People used to die because of poor sanitation conditions in their countries. Another reason was medicines. New medicines helped people heal. And medicines reached far more people that before were not able to get one. This increased the time span people lived. And finally, food production. More and better food were part of the families in those years. They could feed their children and family members better. With better nutrition, more years to live.