Since the 1970s, approximately 40 new infectious disease agents have been discovered, including SARS, chikungunya and zika. The ability of these agents to spread rapidly and cause global concern is due to all of the following except

A. communities are becoming more sparsely populated.

B. individuals are traveling more frequently and farther distances than in the previous half-century.

C. communities are becoming more densely populated.

D. communities are spreading into rural areas/wildlife habitats.