Answer:
D. Factories began to hire more workers in cities
Step-by-step explanation:
US cities began becoming more industrialized.
Industrialization is kind of like upgrading your base in clash of clans. except... its not at all like that of course.
Industrialization was the implementation and economic change in the US (or in any country) during the 18th century. Basically factories started becoming popular and they needed more workers to keep the systems and what not running.
hope this helped :D