Answer:
Letter b
Step-by-step 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.