Answer: D. Machines started to replace workers.
Explanation: D is the correct answer because the use of new machines and technology during the Industrial Revolution led to a significant increase in production capacity, which reduced the cost of manufacturing goods. This meant that many employers could now replace manual laborers with machines, which could perform the same tasks faster and more efficiently. As a result, many workers lost their jobs, and those who remained often had to work longer hours for less pay in harsh conditions.