I believe it is C but I have not learned about this in a while.
I hope this helps and it is not wrong.
The Chinese developed in river valleys that it basically trapped them in short geography
Answer: put a comma after therefore & you’re good
The best answer is D. The Truman doctrine helped to prevent the spread of Communism past the already established boundaries after WWII. The United States would give economic assistance to countries in need so they did not have to turn to a Communist country for assistance. It wasn't just for third world countries, but any independent country in need that the United States felt might have Communist assistance and allow that ideology to expand.