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．Metaphor.
B．Simile.
C．Personification.
D．Imagination.

A．the wonders of travel
B．her growth from an innocent child to a learned woman
C．the benefits of reading
D．the difference between childhood dreams and life's realities