A、Wavelength. B、Lightness. C、Color. D、The number of sources. A

(19)Forget milky drinks, hot water bottles or curling up with a good book. The real secret to a good night’s sleep may be where you sit at work. Not only can the stress of work leave employees tossing and turning, but sitting too far from a window can knock 46 minutes off a normal night’s sleep. Researchers found that workers forced to work in windowless rooms had a poorer quality of life and more irregular sleep patterns than those with access to daylight.(20)The findings, published in the Journal of Clinical Sleep Medicine, suggest the working environment may be crucial to setting the body’s own internal clock. Researchers say better designed offices could boost the physical and mental health of workers. One in three Britons suffers from poor sleep, with stress, computers and taking work home often blamed for the lack of quality slumber. However, the cost of all those sleepless nights is more than just bad moods and a lack of focus. Regular poor sleep raises the risk of serious medical conditions like overweight, heart disease and diabetes—and can even shorten the life expectancy.(21)Independent sleep expert Dr. Neil Stanley said the body needs exposure to daylight to keep its sleeping patterns on track. "light is essentially the thing that tells our bodies to be awake and dark tells them to go to sleep. "(22)The problem with office lighting is that it is not made up of "blue" light, which is the wavelength of light you get from the sun and controls your body clock. " So you could have a very well-lit office but it does not have the same effect because it’s artificial and does not contain blue light. "
19. What is mentioned in the passage as a possible suggestion to have a good night’s sleep?
20. What do the findings published in the Journal of Clinical Sleep Medicine suggest?
21. What role does daylight play in people’s health?
22. What’s the major difference between natural light and office lighting?