The correct answer is B. They would go into small spaces of the machines in factories that adults could not reach.
Explanation
During the time of industrialization, the factories of the urban centers were very important because there was concentrated the greatest producing force of the countries. At this time, most companies employed children to work because their salary was less than that of adult men, and because of their size, they could enter the smaller compartments of the machines. So, the correct answer is B. They would go into small spaces of the machines in factories that adults could not reach.