In $1900,$ approximately $75\%$ of workers worked in manual jobs, like farming and 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?

the decline of white$-$collar professional and service employment in other parts of the world, primarily Asia

the increase in full$-$time paid employment with the same employer over a long period of time

the aging labor force

the introduction of labor$-$saving machinery