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 densely populated. b. communities are becoming more sparsely populated. c. individuals are traveling more frequently and farther distances than in the previous half-century. d. communities are spreading into rural areas/wildlife habitats.

Letter b

Explanation:

The diseases that are common to wild species are becoming more prone to be human diseases since the 1970s. Virus are specially important agents of sources of disease because their nature allows them to spread and adapt to different hosts easily compared to other organisms. After the 1970s the urbanization rate around the world has accelerated and thus most part of the world population it is now allocated on those dense populated areas. Those areas tend to be easy targets for a spreading infectious disease that culminate in global threats.

from my research i have to the conclusion that decomposers, such as fungi, bacteria and invertebrates, play a critical role in nutrient cycling and without them the earth's ecosystem may not support life as we know it. elements such as carbon, nitrogen and phosphorus exist in limited amounts on earth, although huge amounts of carbon are being released into the atmosphere from underground sources now by humans. it is still extremely important that other nutrients be retained by the process of re-use. decomposers are organisms that are able to chemically break down dead material and make these elements available for use by other organisms. without this breakdown of dead material, dead bodies would pile up. so decomposers also play a role in clean up also. without them, life might not continue as we know it and dead material would overwhelm the earth.    

c is the correct answer hope this !