The critical reasoning question is based on a short argument, a set of statements, or a plan of action. For each question, select the best answer of the choices given and explain why the chosen answer is the right fit.

Question: Malaria passes into the human population when a mosquito carrying the malaria protozoa bites a human who has no immunity. The malaria parasite can remain for up to forty days in the blood of an infected person. The disease cannot be passed from person to person, unless a non-infected person is exposed to the blood of an infected person. Theoretically, malaria could be eradicated in any given area, if all the mosquitoes carrying malaria in that area are exterminated. If such a course of action is carried out at a worldwide level, then the global eradication of malaria is possible. 

Which of the following, if true, suggests that the epidemiologist's plan for eliminating malaria is not viable?