洗青菜时，冷水没有变成绿色；把青菜煮沸后，水就变成了的绿色．关键是煮沸后破坏了（  ）

   Everybody dreams. But only some people remember their dreams. Our dreams often include all the senses—smells, sounds, sights, tastes and things we touch.
   Early in the twentieth century, two famous scientists developed their personal ideas about dreams. Austrian psychiatrist(奥地利心理学家) Sigmund Freud believed people often dream about things they want but can’t have. Swiss(瑞士) psychiatrist Carl Jung worked closely with Freud for several years, but he believed dreams provide solutions to problems we face when we are awake.
   Other researchers are studying how dreaming helps our bodies work with problems and very sad emotions(感情). Robert Stickgold is a professor of psychiatry (心理学教授). He says that when we dream, the brain is trying to make sense of the world. He does not agree with Sigmund Freud that dreaming is the way we express our hidden feelings and desires(愿望).
   Scientists believe it is important to keep researching dreams. Yet there is still no agreement on exactly how the brain works when we are dreaming or why we dream.