Question

in october of 1950, un forces pushed the north koreans as far north as
pusan.
the yalu river.
the 38th parallel.
seoul.

Explanation:

In October 1950 during the Korean - War, UN forces pushed the North Koreans back to the 38th parallel. The 38th parallel was the pre - war border between North and South Korea. Pusan was a defensive perimeter earlier, the Yalu River was reached later and led to Chinese intervention, and Seoul had been captured and recaptured multiple times but the significant northern limit reached in October 1950 was the 38th parallel.

Answer:

the 38th parallel.