单选题
Let us begin by saying what does not cause our dreams. Our dreams do not come from "another world." They are not messages from some outside source. They are not a look into the future, either.
All our dreams have something to do with our emotions, fears, longings, wishes, needs and memories. But something on the "outside" may affect what we dream. If a person is hungry, or tired, or cold, his dreams may include a feeling of this kind. If the covers on your body, such as a quilt or a blanket, have slipped off your bed, you may dream that you are sleeping or resting on the ice and snow. The material for the dream you will have tonight is likely to come from the experiences you have today.
So the subject of your dream usually comes from something that has effect on you while you are sleeping (feeling of cold, a noise, a discomfort, etc.) and it may also use your past experiences and the wishes and interests you have now. That is why very young children are likely to dream of fairies, older children of school examinations, hungry people of food, homesick soldiers of their families, and prisoners of freedom.
To show you what is happening while you are asleep and how your wishes or needs can all be joined together in a dream, here is the story of an experiment. A man was asleep and the back of his hand was rubbed with a piece of absorbent cotton (药棉). He would dream that he was in a hospital and his charming girlfriend was visiting him, sitting on the bed and feeling gently his hand!
There are some scientists who have made a special study of why we dream, what we dream and what those dreams mean. Their explanation of dreams, though a bit reasonable, is not accepted by everyone, but it offers an interesting approach to the problems. They believe that dreams are mostly expressions of wishes that did not come true. In other words, a dream is a way of having your wishes carried out.