The correct answer is that the case fatality rate of the Pacific Pox must be high.
A case fatality rate is the ratio of deaths due to a certain disease (throughout the duration of the disease in question). In this scenario, since there are no survivors left, the proportion of deaths among the people who had this disease is obviously rather high.
The answer should be B. Taxation
A possible negative aspect of the elastic clause was that certain powers could not be explicitly given.