What does "them" refer to in the sentence "It sent them streaming westward into the wilderness after their predecessors to raise still more children who wanted still more land"

A．She visited Victorian England and Tsarist Russia.
B．She flew to Los Angeles, Chicago and London with her parents.
C．She read all kinds of books.
D．She spent lots of time traveling on trains.

A．They showed great endurance.
B．They spent a great deal of money.
C．They wanted their own land.
D．They traveled with few possessions.