Answer:
C) Were hired to tend to machines and were paid less than skilled workers.
Step-by-step explanation:
In the Gilded Age, unskilled workers could be hired onto an assembly line to do only one job, repeated over and over again. Since they had no skill, and could be taught quickly and with ease, their work could be seen as invaluable or cheap, so they were paid low wages. Trade workers had jobs that had to be done by hand, or were difficult to accomplish, so they would obviously be paid more than an unskilled worker, who could be replaced easily.
TL;DR -- Unskilled workers worked for cheap on assembly lines because their jobs were simple. I got this question right on the test so, please believe me.