Normally, the pineal gland governs a person’s sleep-wake cycle by secreting melatonin in response to the daily cycle of light and darkness as detected by the eye. Nonetheless, many people who are totally blind due to lesions in the visual cortex of the brain easily maintain a 24-hour sleep-wake cycle. So the neural pathway by which the pineal gland receives information from the eye probably does not pass through the visual cortex.

For purposes of evaluating the argument it would be most useful to establish which of the following?

(A) Whether melatonin supplements help people who have difficulty maintaining a 24-hour sleep cycle to establish such a pattern

(B) Whether the melatonin levels of most totally blind people who successfully maintain a 24-hour sleep-wake cycle change in response to changes in exposure to light and darkness

(C) Whether melatonin is the only substance secreted by the pineal gland

(D) Whether most people who do not have a 24-hour sleep-wake cycle nevertheless have a cycle of consistent duration

(E) Whether there are any people with normal vision whose melatonin levels respond abnormally to periods of light and darkness

题目类型：

evaluate the argument

题目翻译：

通常，PG通过分泌M来控制一个人的睡-醒循环，而M是眼睛所探测到的光暗的反应。然而，许多因为大脑视觉皮质受到损伤致盲的人可以很容易地维持24小时的睡-醒循环。所以，从眼睛到PG的神经传导可能不通过大脑的视觉皮质。以下哪一项最有助于评估这段论述的正确性?

解题思路：

无既定思路，逐项分析。

逐项分析：

A、M并非越多越好，补充M有可能导致过量，故无法得出确切结论，排除。

B、正确选项。符合题干主旨。

C、M是不是PG分泌的唯一物质。无关项。

D、没有24小时睡-醒循环的人是不是有他们特定的周期。无关项。

E、对光暗的异常可能有很多原因，不一定是视觉皮质引起的，排除。

正确选项：

B