【正确答案】 B

【答案解析】 Argument Evaluation
   Situation  Normally, a person's sleep-wake cycle is governed by the pineal gland secreting melatonin in
              response to the daily cycle of light and darkness as detected by the eye. Yet many people who are
              totally blind due to lesions of the visual cortex easily maintain a 24-hour sleep-wake cycle.
   Reasoning  What additional information would be most helpful in evaluating the argument? The argument's
              conclusion is that the neural pathway by which the pineal gland receives information probably
              does not pass through the visual cortex. This is suggested by the fact that people without a
              well-functioning visual cortex (e.g., people with a certain type of blindness) can nonetheless
              maintain a 24-hour sleep-wake cycle. Is it by the pineal gland's secretion of melatonin that they
              do so? The argument tells us that normally (i.e., in sighted people), this is the mechanism for
              sleep regulation. But the argument depends on assuming that a similar mechanism is operating
              in people who are blind but have well-regulated sleep cycles. The best choice will be the one that
              helps us decide whether that assumption is correct.
   A   This question would not give us an answer that would help in evaluating the argument. A "no" answer would not clarify whether the pineal gland-melatonin mechanism operates in people who are blind. A "yes" answer would do no better. The question refers only to people who have sleep dysfunctions (which the argument does not address).
   B   Correct. Answering this question would provide the most useful information for evaluating the argument. A "yes" answer would help confirm a key assumption of the argument: that blind people rely on the pineal gland-melatonin mechanism for sleep regulation. A "no" answer would help disconfirm that assumption.
   C   Whether or not there are other substances secreted by the pineal gland makes no difference to the reasoning. The argument relies on the premise that the pineal gland governs the sleep cycle by secreting melatonin. For example, if the pineal gland sometimes secreted adrenaline, that would still have no bearing on the argument.
   D   The consistency or inconsistency of the duration of some people's sleep patterns has no relevance to the reasoning. Their sleep patterns could be due to any of a number of factors.
   E   This does not help, for there could be sighted people whose melatonin levels respond abnormally simply because of a pineal-gland abnormality.
   The correct answer is B.