Why would Nigeria, as opposed to a nation like the United States, be a more likely location of a medical emergency, like the one described in the excerpt?

A Doctors must receive special permission from the United Nations to practice in African nations, and receiving permission is costly and time-consuming.
B African nations have trade restrictions that make the availability of medicines an issue.
C Most doctors refuse to serve in Africa, due to racism and religious difference.
D Nations, like Nigeria and other developing countries, lack enough quality resources to provide proper health care services.