Cross-text Multiple Matching

Part 6
You are going to read extracts from articles in which four experts discuss the reasons why animals, including humans, sleep. For questions 37-40, choose from the experts A-D. The experts may be chosen more than once.
Why do we sleep?
A
Although an average human spends a third of their life sleeping, there are great variations in how much time other animals devote to it. For some, it appears to be remarkably little, though there is clear evidence that all species do spend some time asleep. As many major bodily restorative functions occur almost entirely during that time, it seems reasonable to conclude that this is the principal purpose of sleep. The benefits to the human memory of sleep still need to be assessed accurately and conclusively, however, and may indeed have been overrated. Indeed, some assert – though the findings they cite are unconvincing – that sleep is merely something that animals are able to enjoy when they have no more pressing needs, such as eating or reproducing. In many circumstances, or so they say, sleeping may simply be a less dangerous choice than roaming around and exposing oneself to predators.   However, evidence to support this view remains sparse at best.
B
Most experts believe that sleep is a universal requirement in animals, and I would not differ from that viewpoint. It is nevertheless true that nobody has yet identified the core function of sleep. Sleeping at night or day was very probably an adaptation for survival at a