In the Distant Past, Infectious Diseases Could Have Substantial Impact

In the distant past, infectious diseases could have substantial impact on

A) foreign populations or groups, but seldom significantly impacted large regions or areas.
B) foreign populations or groups and often significantly impacted small regions or areas.
C) local populations or groups, but seldom significantly impacted large regions or areas.
D) local populations or groups and often significantly impacted large regions or areas.