Which of these is a compound sentence?

Question

Immigrants who came to work in factories lived in urban neighborhoods.
“Old” immigrants often settled on farms, but most “new” ones lived in cities.
In the past, many immigrants had come from Northern and Western Europe.
Immigrants working long hours and facing crowded living conditions.

Answer 1

The compound sentence among the options is:

“Old” immigrants often settled on farms, but most “new” ones lived in cities.

This sentence contains two independent clauses joined by the coordinating conjunction "but."