Directions: The questions in this section are based on the reasoning contained in brief statements or passages. For some questions, more than one of the choices could conceivably answer the question. However, you are to choose the best answer; that is, the response that most accurately and completely answers the question. You should not make assumptions that are by commonsense standards implausible, superfluous, or incompatible with the passage. After you have chosen the best answer, blacken the corresponding space on your answer sheet.
Studies have shown that treating certain illnesses with treatment X produces the same beneficial changes in patients’ conditions as treating the same illnesses with treatment Y. Furthermore, treatment X is quicker and less expensive than treatment Y. Thus, in treating these illnesses, treatment X should be preferred to treatment Y.
Which one of the following, if true, would most weaken the argument above?
A． Unlike treatment Y, treatment X has produced harmful side effects in laboratory animals.
B． There are other illnesses for which treatment Y is more effective than treatment X.
C． Until recently, treatment X was more expensive than treatment Y.
D． Treatment Y is prescribed more often by physicians than treatment X.
E． A third treatment, treatment Z, is even quicker and less expensive than treatment X.