阅读短文，选出填入空格最合适的一项： Many people believe t…

阅读短文，选出填入空格最合适的一项：

Many people believe that working longer hours makes them more productive. However, a growing body of research suggests the opposite. In one study, employees who worked more than fifty hours a week produced little more than those who worked forty. After a certain point, extra hours simply led to more mistakes and greater ___. The researchers concluded that rest is not a waste of time but a necessary part of doing good work.