Epidemiologist: 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? ['A person who is infected with malaria can infect a mosquito that is not carrying malaria, if that mosquito bites such a person.', 'Malaria is still endemic in many parts of the world, and many health workers believe that the global eradication of malaria is not possible.', 'Some people in areas where malaria is rife have developed an immunity to mosquitos, yet they also show a higher incidence of genetic disorders such as sickle-cell anemia.', 'Unless a mosquito bites an infected person, and then bites a non-infected person, malaria cannot be passed directly from human to human.']