Exercise 8 - Part 2
For questions 1-8, think of the best word that fits each gap. Use only one word in each gap. All answers must be in lowercase.
Some of the gaps might have more than 1 answer, in that case, the system will detect it as incorrect, but will provide all the possible answers.
The truth (1) nobody really knows the exact evolutionary reason why we spend a third of our lives asleep. Did we all develop this habit at around the same time (2) of the manner in which our brains had begun to process complex memories? Although there is a lack of clear evidence, scientists have come up with various theories. One recent theory is that human beings have evolved in (3) a way that we clear out toxic waste from the brain during deep sleep. In (4) words, sleep came about as a crucial maintenance process. Cognitive function (5) well be programmed to require this downtime but, (6) this, many people still choose to sacrifice rest for work. This research shows, if (7) else, that sleep is a biological necessity, not something we can simply learn to live (8) .
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