Answer:
b. Emerging and reemerging disease
Explanation:
Emerging and reemerging disease are infectious diseases which showed growth in last two decades by targeting large populations, spreading in many geographical areas and demonstrating an increased fatality rate. For example, Ebola and HIV AIDS.
These infections emerged because of presence of many favorable factors at the same time. Increasing population made it easier for the infection to spread because it is difficult to maintain a distance between people now. Increase in global travel also increased the chances of contacting the virus as the carrier can take it to a new unaffected region. Change in temperature also made it favorable for many viruses to propagate.