I'm not exactly clear on what your question is here. But, I'm going to assume from your title that you'd like to know why answer choice (B) is not the correct answer.
The historical fact that the passage is referring to is, "The United States has never been a great international trader. It found most of its raw materials and customers for finished products within its own borders."
These statements are not opinions or points of view. They merely state facts on the history of the United States and how they received their raw materials and customers.
Therefore, answer choice (B) is something the author did mention in order to advance her point of view.
Hope that helped! Let us know if you have any other questions.
