Another difficult CR

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 under-
mines 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.

I think the answer is E, rite?