听力原文： A United Nations agency has issued an urgent appeal for more international aid to help stop an upsurge of desert locust swarms from becoming a plague. The Food and Agriculture Organization says the upsurge is the worst in fifteen years. Large swarms have moved from their spring breeding areas in northwest Africa to Mauritania, Senegal and Mali. The organization says the locusts are likely to spread as far as Niger and Chad, and could even reach Darfur in western Sudan. A BBC science correspondent says major insecticide spraying programs have been initiated, some funded by western donors, but clearly they haven't worked.
What plague are some African countries facing？

A. Quick spread of the desert.
B. Quick spread of an insect.
C. Upsurge of an infectious disease.
D. Overflowing of a river.