In malaria-infested areas, many children tend to suffer several bouts of malaria before becoming immune to the disease. Clearly, what must be happening is that those children's immune systems are only weakly stimulated by any single exposure to the malaria parasite and need to be challenged several times to produce an effective immune response.

Which of the following, if true, most seriously undermines the explanatory hypothesis?

(A) Immediately after a child has suffered a bout of malaria, the child's caregivers tend to go to great lengths in taking precautions to prevent another infection, but this level of attention is not sustained.
(B) Malaria is spread from person to person by mosquitoes, and mosquitoes have become increasingly resistant to the pesticides used to control them.
(C) A certain gene, if inherited by children from only one of their parents, can render those children largely immune to infection with malaria.
(D) Antimalaria vaccines, of which several are in development, are all designed to work by stimulating the body's immune system.
(E) There are several distinct strains of malaria, and the body's immune response to any one of them does not protect it against the others.

Please explain each choice. Thank you