A. more cases are now reported because of increases in administrative efficiency
B. a very high proportion of the cases were in people who had recently returned from neighboring cities
C. an effective diagnostic test was introduced about two months ago
D. the disease is prevalent only in some industrialized cities which have shown a dramatic increase in population due to migration
E. the incidence (number of cases per thousand) of dengue, also contracted from mosquito bites, has increased
Explanation: The conclusion is that the mosquito control measures *failed*. To **cast doubt** on this, you need an alternative explanation for the increase in cases. Options 1, 2, 3, and 4 all provide alternative reasons (better reporting, imported cases, new test, more people to infect). Option 5, the increase in dengue incidence (another mosquito-borne disease), *supports* the authority's conclusion that the mosquito control measures are failing, thus it is the one statement that would **NOT** cast doubt on the conclusion.
