Answer: A. The American government tried to intervene there before it got to the other places.
Step-by-step explanation:
You included no picture as a reference for the question but the above should be correct.
The American policy in South-East Asia was dictated by something called "The Domino Theory".
Simply put, it stated that for communism to spread in that part of the world, one country needed to fall to communism and then push the others towards it.
The U.S. therefore wanted to stop it as soon as possible to prevent it from spreading to the other countries in the region.
This is why they got involved in Korea and Vietnam.