Red blood cells in which the malarial-fever parasite resides are eliminated from a person's body after 120 days. Because the parasite cannot travel to a new generation of red blood cells, any fever that develops in a person more than 120 days after that person has moved to a malaria-free region is not due to the malarial parasite.

Which of the following, if true, most seriously weakens the conclusion above?

• AThe fever caused by the malarial parasite may resemble the fever caused by flu viruses.  
• BThe anopheles mosquito, which is the principal insect carrier of the malarial parasite, has been eradicated in many parts of the world.  
• CMany malarial symptoms other than the fever, which can be suppressed with antimalarial medication, can reappear within 120 days after the medication is discontinued.  
• DIn some cases, the parasite that causes malarial fever travels to cells of the spleen, which are less frequently eliminated from a person's body than are red blood cells.  
• EIn any region infested with malaria-carrying mosquitoes, there are individuals who appear to be immune to malaria.