Compared with dreamless sleep, deep dream sleep is
A、not the result of natural selection
B、less likely to appear to monkeys
C、more protective to the animals
D、at a higher stage of evolution
Task 116. Paragraph① 17. Paragraph② 18. Paragraph③ 19. Paragraph④ 20. Paragraph⑤ A. Lightening Causes Puzzles to PeopleB. Types of LightningC. Causes of LightningD. Differences Between Thunder and ThunderstormE. Frequencies of Thunderstorms Occurring in the Worldand the U. S. F. Shock Waves as Thunder