In 1870, horses and mules were the prime source of power on U.S. farms. One horse or mule was required to support four human beings—a ratio that remained almost constant for many decades. At that time, had a national commission been asked to forecast the horse and mule population for 1970, its answer probably would have depended on whether its consultants were of an economic turn of mind. Had they been "economists", they would have recognized that the power of steam had already been harnessed to industry and to land and ocean transport. They would have recognized further that would be only a matter of time before steam would be the prime source of power on the farm. It would have been difficult for them to avoid the conclusion that the horse and mule population would decline rapidly.
Which of the following is NOT mentioned by the author as a consequence of new technological developments？

A. Older technologies die away.
B. The quality of life is improved.
C. Overall productivity increases.
D. More raw materials become necessary.