[解析]
(1)细节理解题。根据第三段中的But that all changed on day six,when participants reported that the severity of physical symptoms was at its worst. (但在第六天,所有这些都发生了变化,当时参与者报告说身体症状的严重程度处于最糟糕的状态。)可知,在第六天参与者的身体症状最糟糕。故选C。
(2)细节理解题。根据第四段中的However,results from this study show that having just one night of sleep loss can significantly weaken your daily functioning. (然而,这项研究的结果表明,仅仅一晚的睡眠不足就可以显著削弱你的日常功能。)可知,即使一晚的睡眠不足也会影响我们的日常表现。故选C。
(3)细节理解题。根据倒数第二段These negative feelings and symptoms were continuously sharpened throughout continuous sleep loss days and didn't return to baseline levels unless they had a night sleep of more than six hours. (这些消极的感觉和症状在连续睡眠不足的日子里不断加剧,除非他们晚上的睡眠超过6小时,否则不会恢复到基线水平。)及最后一段Lee says the best way to maintain a strong daily performance is to set aside more than six hours to sleep every night. (Lee说,保持良好的日常表现的最好方法是每晚留出六个小时以上的睡眠时间。)可知,要解决因睡眠不足引起的问题就需要每晚留出六个小时以上的睡眠时间。故选D。
(4)主旨大意题。根据第一段All it takes is three continuous nights of sleep loss to cause your mental and physical well﹣being to greatly worsen. (只要连续三个晚上睡眠不足,你的身心健康就会大大恶化。)以及下文关于睡眠不足实验结果的描述可知,文章主要讲缺乏睡眠会对我们的身心造成影响,B项The consequences of sleep loss."睡眠不足的后果"概括文意。故选B。