单选题：根据以下内容回答题：In recent years many countries of the world have

根据以下内容回答题：
In recent years many countries of the world have been faced with the problem of how to make their workers more productive．Some experts claim the answer is to make jobs more varied．But do more varied jobs lead to greater productivity?There is evidence to suggest that while variety certainly makes the worker's life more enjoyable，it does not actually make him work harder．As far as increasing productivity is concerned，then variety is not an important factor．
Other experts feel that giving the worker freedom to do his job in his own way is important and ther6 is no doubt that this is true．The problem is that this．kind of freedom cannot easily be given in the modern factory with its complicated machinery which must be used in a fixed way．Thus while freedom of choice may be important，there is usually very little that can be done to create it．Another important consideration is how much each worker contributes to the product he is making．In most factories the worker sees only one small part of the product．Some car factories are now experimenting with having many small production lines rather than a large one so that each worker contributes more to the production of the cars on his line．It would seem that not only is degree of worker contribution an important factor，therefore，but it is also one we can do something about．
To what extent does more money lead to greater productivity?The workers themselves cer-tainly think this important．But perhaps they want more money only because the work they do is so boring．Money may explain demands for shorter working hours．Perhaps if we succeed in making their jobs more interesting，they will neither want more money，nor will shorter working hours be so important to them．
Which is NOT the possible factor leading to greater productivity? A．To make jobs more varied．
B．To give the worker freedom to do his job in his own way．
C．Degree of work eontrib．ution．
D．Demands for longer working hours．