A、British. B、Americans. C、Germans. D、Japanese. CWho firstly used flexible working hours? 信息明示题。由文章开头可知，灵活工作时间机制由德国人发明，所以C正确。

Flexible working hours were invented in Germany in the late 1960s, but reached Britain in 1972. The system allows workers to start and finish work whenever they want, with only two requirements. These are: firstly, that all workers must be present for certain "key" times in the day, and secondly, that all workers must work the agreed total number of hours per week.
   The system has proved an almost total success wherever it has been tried. A survey of 700 workers on flexible hours showed three main advantages: a better balance between working and private life, avoidance of the need to travel during rush hours and the ability to be able to finish a certain task before leaving.
   From the employer’s point of view, the system tends to increase productivity, reduce labor turnover first. "Flexible time" was mainly confined to white-collar workers, but it is now being applied to manual workers too.