Well there's no answer since a virus is something that can't be cured for a while and takes years to find a cure since they are new and need time to be assessed and the human body to build a resistance against. However in terms of how many deaths, this virus has caused 1.32 Million deaths so I guess you could say this is the most deadly, in a while. Aside from the deaths more than half of the patients have been cured.
The correct answer is this one: "human industrialization." Air pollution comes from human industrialization. Because of too much industrialization, there are a lot of excess and wastes in any form: air or even liquid and solid wastes.
