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? ['The fever caused by the malarial parasite may resemble the fever caused by flu viruses.', 'Many malarial symptoms other than the fever, which can be suppressed with antimalarial medication, can reappear within 120 days after the medication is discontinued.', 'The anopheles mosquito, which is the principal insect carrier of the malarial parasite, has been eradicated in many parts of the world.', "In 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."]