The answer you are looking for is B. "Increased Life Expectancy".
Self-government is a government in which the people govern the country. This would cause societal and governmental issues or challenges, because people may abuse their power in a self ruled government.
Terrorism would cause challenges, because it interferes with the security of people, and may even cause harm or death to citizens in region.
Increased global population would cause challenges, because that could potentially lead to over-crowding and an increase in homelessness. This could also bring an increase of crime to poorer areas.
Thus making increased life expectancy the answer. I hope this helps!
