Final answer:
The correct answer to the question is D. both b and c, which refers to HIV that causes AIDS and the H1N1 influenza virus strain. Both viruses have appeared and spread rapidly, meeting the WHO criteria for emerging viruses.
Step-by-step explanation:
An example of an emerging virus is HIV that causes AIDS and a strain of influenza virus called H1N1 that causes the flu. So, the correct answer is D. both b and c.
HIV (Human Immunodeficiency Virus) was identified in the early 1980s and fits the criteria of an emerging virus as it has spread rapidly across geographic ranges and has substantially increased in population impact, leading to the pandemic of AIDS.
Influenza H1N1 is another example of an emerging virus that caused a global pandemic in 2009, historically known as swine flu. This virus is particularly notable for its ability to undergo antigenic drift and shift, leading to new strains that can infect humans.