Read the following passage and mark the letter A, B, C, or D on your answer sheet to indicate the correct answer to each of the questions. 

     People who daydream are often thought of in negative terms, such as being lazy or not doing what they should be doing. However, scientists who study the brain have learned many interesting things, especially from studying the brains of daydreamers. In fact, far from being a waste of time, some scientists believe that daydreaming is a healthy and useful activity for all of our brains. 

     In order to study the brain, scientists use special devices that scan the brain and show pictures of which parts of the brain are active at certain times. By using this technique, they proved that when a person is daydreaming, the device will show a distinct pattern of activity in the brain called the "default" mode of thinking. In the default mode, the top or outside part of the brain is very active. Actually, several regions of the brain are interacting in this mode. Some scientists describe this mode as a time when the brain focuses on itself rather than focusing on the environment around the person. Typically, this occurs when a person is doing simple, tedious work or performing routine actions that don't need much attention, like walking to school or cooking simple foods. People tend to daydream during such activities. 

     The importance of daydreaming lies in developing both creative and social skills. When the mind is not engaged in dealing with one's immediate situation or problem, then it is free to wonder about things. A time of wandering allows the mind to create things. New inventions may be imagined, or possible solutions to a problem can be planned. For example, solutions for problems in relationships with other people may come to mind. In fact, most daydreams involve situations with others. Perhaps these are daydreams based on memories of the past, or daydreams of what might be in the future. In either case, daydreams help us develop the appropriate skills we can use in real interactions with others. 

     As neurologist Dr. Marcus Raichle of Washington University explains: "When you don't use a muscle, that muscle really isn't doing much. But when your brain is supposedly doing nothing and daydreaming, it's really doing a tremendous amount." During the so-called "resting state" the brain isn't resting at all!

What does the passage mainly discuss?