Why 1 do we sleep(we/ sleep)? From birth, we 2(spend) a third of our lives asleep but scientists still 3(not/ know) exactly why. Why 4(humans /have) problems sleeping? In modern society, many people 5(not /get) the recommended seven or eight hours a night. We 6(work) long hours and we rarely 7(go) to bed at sunset. Why8(we/ sleep) different?It 9(depend) on the time of year and also our age. Teenagers always10(need) more sleep than adults Lots of elderly people 11(not/ sleep) longer than four or five hours, bu they often 12(take) naps during the day.