As part of its policy of "containment" during the cold war, the united states hoped to keep communist influence in korea
a. south of the yalu river. eliminate
b. south of the mekong delta.
c. north of the 38th parallel.
d. north of the 17th parallel.

The answer is c. north of the 38th parallel. President Truman told MacArthur to keep the conflict within the 38th parallel.  However when they push the North Koreans out of the South, they crossed over this boundary.  This caused the Chinese to launch an attack that further complicated the war.