You have waited 45 minutes for the valuable 10 minutes' break. But when the bell for the next class rings, you can't believe how quickly time has passed. If you have this experience, you'll know how time flies when you are having fun and _ when you are bored. Now scientists have come up with a reason why this happens. They have found that the brain changes its way to work according to how we direct our attention to a task. When we are bored, we pay more attention to how time is passing. And this makes our brains think the clock is ticking more slowly. Recently some researchers who want to understand the conditions carried out an experiment. In the experiment, twelve volunteers watched a picture while researchers monitored their brain activity. The volunteers were told to first notice how long a picture appeared, then the color of the picture, and thirdly, study the both. The results showed that the brain was more active when the volunteers paid attention to more subjects. It is thought that if the brain is busy noticing many aspects of a task, it has to spread its resources, and pays less attention to the clock. Therefore, time seems to go quickly. If the brain is not so active, it spends its full energy on the passing of time. As a result, time seems to move slowly. Next time you feel bored in class, perhaps you should concentrate  on what the teacher is saying. Which is the best title of the passage?
The best way to save time The importance of planning time Why time passes quickly The reason for time flying and dragging