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?
58. 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?
(A) The fever caused by the malarial parasite may resemble the fever caused by flu viruses.
(B) The anopheles mosquito, which is the principal insect carrier of the malarial parasite, has been eradicated in many parts of the world.
(C) Many malarial symptoms other than the fever, which can be suppressed with antimalarial medication, can reappear within 120 days after the medication is discontinued.
(D) 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.
(E) In any region infested with malaria-carrying mosquitoes, there are individuals who appear to be immune to malaria.
Argument Evaluation
Situation The malarial-fever parasite lives in red blood cells, but these cells are eliminated after 120 days. If the infected person moves to a malaria-free region, any new fever that occurs after 120 days cannot be due to the malarial-fever parasite. Reasoning What weakens the conclusion? The passage says that the malarial parasites that reside in red blood cells are eliminated after 120 days. What if malarial parasites can also reside in other places in a person’s body? If for instance the parasites can reside in the spleen, from which they are not eliminated as frequently, as well as in red blood cells, they may not be eliminated within 120 days. Therefore, they could cause malarial fever after the 120-day period. In that case, the conclusion ruling out a new generation of malarial parasites as the cause of new fever is unfounded.
A The issue is not about a similarity of symptoms but about where the parasites reside.
B The existence of malaria-free regions is not in question.
C The argument gives no reason to postulate any significant connection between the discontinuation of medication and the issue of whether symptoms can persist after a patient has been in a malaria-free region for 120 days.
D Correct. This statement properly identifies a point that weakens the conclusion.
E This tells us only that some individuals are immune; it does not help us determine whether those who are not can have symptoms occur more than 120 days after moving into a malaria-free area.