In 1900,approximately Three-Quarters of the Employed Population Was in Manual

In 1900,approximately three-quarters of the employed population was in manual work,either farming or blue-collar work such as manufacturing.In 2016,the manufacturing workforce was only 8 percent,while white-collar professional and service employment accounted for 80 percent.What is a reason for the transformation of the occupational structure in the United States?

A) the introduction of labor-saving machinery
B) the decline of white-collar professional and service employment in other parts of the world,primarily Asia
C) the increase in full-time paid employment with the same employer over a long period of time
D) the aging labor force