Final answer:
During the last quarter of the 19th century, large numbers of immigrants were admitted to the United States primarily as C) unskilled factory workers.
Step-by-step explanation:
The large numbers of immigrants that were admitted to the United States during the last quarter of the 19th century were primarily needed as C) unskilled factory workers.
As the United States saw a rise in industrialization and the need for workers in factories and mines, millions of immigrants from Europe, including southern and eastern European countries, arrived seeking work and better economic opportunities. The majority of these immigrants were peasant farmers and displaced craftspeople. They settled in urban centers where factories were located and formed immigrant communities, keeping their cultures alive.