Answer:
Option B: The U.S was destined to expand westward and spread civilization.
Step-by-step explanation:
Using the system of trial-and-error, you know that options C and D aren't the correct answers to the question, as the quote says nothing about land, nor about Native American tribes.
For the remaining two choices, Turner said nothing about the Americans becoming weaker with Western life – nor did he even mention any hardships! And so, with the three choices cancelled out, option B seems to be the best answer to this question.