Scientists have come up with a theory for why time flies when you are having fun and drags when you are bored. Scans have shown that【C1】______ of activity in the brain change depending on how we focus on a task. Concentrating on time passing, as we do when bored, wil【C2】______ brain activity which will make it seem as though the clock is ticking more【C3】______ . The research, by the French Laboratory of Neurobiology and Cognition, is published in the magazine Science. In the study, 12 volunteers watched an image while researchers【C4】______ their brain activity using MRI(核磁共振成像) scans. Volunteers were given a【C5】______ of tasks. In one they were told to concentrate simply on the duration of an image, in【C6】______ they were asked to focus on the【C7】______ , and in a third they were asked to concentrate on both duration and color. The results showed that a network of brain regions was【C8】______ when more subjects were paid attention to duration. It is thought that if the brain is busy focusing on many aspects of a task, then it has to spread its resources thinly, and pays less【C9】______ to time passing. Therefore, time passes without us really【C10】______ it, and seems to go quickly.【C11】______ , if the brain is not stimulated in this way, it concentrates its【C12】______ energies on monitoring the passing of time. This may make time seem to【C13】______ , but in fact it is probably a more accurate perception of reality.【C14】______ the researchers found that the more volunteers concentrated on the duration of the images, the more【C15】______ were their estimates of its duration. Lead researcher Dr. Jennifer Coull said many of the areas of the brain【C16】______ in estimating time were the same that played a key role in controlling movement, and【C17】______ for action. She said this overlap suggests that the brain may make sense of time as【C18】______ between movements, in much the same way【C19】______ musicians mark time with his foot, or【C20】______ anticipate the sound of a starter's pistol. 【C1】