Question

which of the following could affect human population? an ethnic war breaks out in eastern Europe a lunar eclipse occurs a deadly virus starts a pandemic a tornado touches down in an uninhabited area in the Midwest prairie

Answer 1

the one that is most likely to affect the human population as a whole is this one:
deadly virus starts a pandemic - this is likely to affect the biggest portion of the human population.

Answer 2

An event that affects human population must put in danger to a big part of the global population and not only to a certain region, therefore an ethnic war in eastern Europe or a tornado in an uninhabited area in the Midwest are not dangerous for humankind. Likewise, lunar eclipses have happened throughout human history, so it's not dangerous either. Conversely, a deadly virus starts a pandemic represents a real danger for all of our lives. Thankfully, vaccines have helped to erase and protect humans, but nowadays some deseases produced by viruses are becoming a threat because fewer people are using vaccinations.