Passage 1

1.C。由“Consistently sleeping six to eight hours per night may be optimal for health.”可知，睡眠时间在六到八小时之间对身体有好处，故答案为C。

2.D。由“They pointed out that previous studies had shown that sleep deprivation was associated with heart disease，high blood pressure，obesity，type 2 diabetes，and high cholesterol.”可知，长期睡眠不足与心脏病、高血压、肥胖、Ⅱ型糖尿病和高胆固醇相关联。但是与肺结核无关，故答案为D。(https://www.daowen.com)

3.D。由“Whilst short sleep may represent a cause of ill-health，long sleep is believed to represent more an indicator of ill-health.”可知，睡眠过短可能是疾病产生的原因，但睡眠过长却更有可能是存在疾病的指示器。故答案为D。

4.A。Whilst在文中是什么意思？A选项“虽然，即使”；B选项“而且，此外”；C选项“因为”；D选项“因为，既然”。根据语境可知Whilst的意思应是“虽然”，故答案为A。

5.A。全文都在探讨睡眠时间长短与健康的关系，故答案为A。