The Southeastern United States Lies in the Heart of the "Horse

Multiple Choice

The southeastern United States lies in the heart of the "horse latitudes" where normally we would expect desert conditions.Why isn't this area a desert?

A) Continental polar air masses disturb the pattern by periodic influxes of cold air.
B) Maritime polar air masses disturb the pattern by driving pacific moisture across North America.
C) Continental tropical air masses derived from Mexico disturb the pattern when these air masses are drawn northward by cyclonic storms.
D) Maritime tropical air masses derived from the Gulf of Mexico disturb the pattern when these air masses are drawn northward by cyclonic storms.