【多选题】

Although it is almost always taken for granted, sleep is an essential part of most creatures’ lives. For giraffes, two hours a day is enough. For bats, however, that number is closer to 20! For human adults, the need averages between seven and eight hours a night, and if they do not get it, they can suffer in their ability to concentrate and to think logically. While humans sleep, a number of things occur. First, their bodies are resting and reenergizing for the next day. Second, their brains are sorting through information and retaining some details while discarding others. Some experts believe this process helps to strengthen individuals’ memories. Third, humans dream.

Dreams have lent an ineffable quality to sleep. While modern scientists believe that dreams are the brain’s method for sifting through life’s daily events, this was not always the case. Long ago, philosophers and sages gave prophetic significance to dreams.Even the ever-practical ancient Romans thought that dreams could be messages sent directly from one of their gods.
Select the sentence within the passage that illustrates a possible minimum level of sleep necessary for full functionality in the animal worlD、