Explain the Primary Source of Recent Cuts to the Number

Explain the primary source of recent cuts to the number and pay of American blue-collar manufacturing jobs.

A) Many such jobs have been outsourced to East Asia, where production costs are low.
B) American manufacturing jobs wax and wane with bubbles in the financial industry.
C) Blue-collar workers have traditionally depended on manufacturing industries, now in decline due to technological innovations.
D) More and more jobs are rendered obsolete with increases in computerized and robotic manufacturing.