The factor that BEST explains the recent increase in the number of undocumented teenage immigrants in the United States from Central American countries is:
D: Escalating gang violence
Escalating gang violence in Central American countries, particularly in the Northern Triangle (Honduras, El Salvador, and Guatemala), has been a significant push factor, driving many teenagers to flee their homes in search of safety and a better life. While factors such as family reunification and economic opportunities also play a role, the immediate threat posed by violence is often the most compelling reason for their migration.