Question

why did railroad expansion increase the populations of major urban centers during the gilded age?
new networks in the rural west allowed more farming.
traveling to different cities and factories became easier.
traveling between the north and the south became easier.
new networks linked canadian and us cities.

Explanation:

During the Gilded Age, urban centers grew because they housed factories and job opportunities. Easier travel via railroads allowed people to move to these cities and access factory work directly, driving population growth. Other options relate to regional connections or farming, not direct urban population growth from migration for urban jobs.

Answer:

Traveling to different cities and factories became easier.