A major new development in system of work in Britain is taking place. Flexible working hours, or "Flextime", are catching on fast, and trend is continuing. In 1973, over 500 organizations had adopted the idea, and by 1974, this number had risen to over 200,000. Flexible working hours were invented in Germany in the late 1960's, but reached Britain only 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 present for certain "key" times in the day, and secondly, that all workers must work an agreed total number of hours per week. The system had proved a 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 finish a certain task before leaving. From the employer's point of view, the system tends to increase productivity, reduce labour turnover and give workers a greater sense of duty. At first, "Flexible" was mainly confined to white-collar workers, but it is now being applied to manual workers too. Key time is a period when   _  .
visitors come to the plants all workers must be at work employers go round in the workshop rush hours are over
Question: A major new development in system of work in Britain is taking place. Flexible working hours, or "Flextime", are catching on fast, and trend is continuing. In 1973, over 500 organizations had adopted the idea, and by 1974, this number had risen to over 200,000. Flexible working hours were invented in Germany in the late 1960's, but reached Britain only 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 present for certain "key" times in the day, and secondly, that all workers must work an agreed total number of hours per week. The system had proved a 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 finish a certain task before leaving. From the employer's point of view, the system tends to increase productivity, reduce labour turnover and give workers a greater sense of duty. At first, "Flexible" was mainly confined to white-collar workers, but it is now being applied to manual workers too. Key time is a period when   _  .
A. visitors come to the plants
B. all workers must be at work
C. employers go round in the workshop
D. rush hours are over
Answer: