Ответ:
Why do we sleep?
From birth, we spend a third of our lives asleep, but scientists still do not (don't) know why.
Why do we have problems sleeping?
In modern society, many adults do not (don't) get the seven or eight hours sleep the need every night. We work long hours and we rarely go to bed at sunset.
Why do we sleep differently?
It depends on the time of year and also our age. Teenagers usually need more sleep than adults. Lots of elderly people do not (don't) sleep longer than four or five hours at night, but they often take naps during the day.
Объяснение:
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