Humans are programmed to wake and sleep on a roughly 24-hour cycle, and the timing is regulated by exposure to light. According to a statement from the Healthy Homes project: “ Disruption of a regular, daily pattern of light and dark can lead to poor sleep, fatigue and decreased performance, as well as poor health ranging from obesity, diabetes, cardiovascular disease and even cancer. ” In places where sunlight is in short supply, bright electric lighting delivered at the right time of day can act as a substitute. “We anticipate that this will make it easier for people, especially people working within shift work, to have better lighting solutions in their home, ’’ says Prof Laike. “But also people who have problems coming up in the morning during the dark period. Because we know that in those countries far from the equator such as Sweden, we have a need for light especially in the morning. ” Prof Laike believes architects also need to re-examine and perhaps re-employ the building standards of the 19th century when designers were obliged to maximize the amount of daylight penetrating schools and factories.

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以下问题只用到以上这一段内容：

问题： Human beings need sunlight exposure especially in the morning because .

A. their body clock would stop regulating work at night

B. the sunlight regulates certain hormone to keep people energetic

C. the morning sun gives off the full spectrum of rays

D. the 19th century architects had already found it necessary to maximize the sun penetration

答案是不是选A？