I think your right the answer should be C
The are many reasons why the USA got involved in the Korean War. The main reason is because, during that time, Communism had become an opponent for the democratic government. Thus, when North Korea became Communists, they decided to intervene to undermine Communism and protect the American way of life (during this time period, America was very scared of Communism taking over). The other two reasons are a) in fear of the 'domino theory' (do look it up) and they were in competition for world domination with (at the time) the USSR.
Search this again a person on a different one has all the answers idk if they are right though
james poliver of mintoina