Today, we know that the climate history over the last 10.000 years has been drastically changing. One particularly important aspect on what had happened was the fact that the glaciers and ice caps melted - a.
This has been happening over the thousands of years and has been increasingly noticeable in the last couple of decades.
Signs point to North Korea unilaterally launching the invasion. It was not helpful for the USSR and was at a very bad time for the PRC since the war immediately shut down plans to invade Taiwan.
The U.S., especially after Chinese troops entered the war, viewed it as a united and aggressive communist bloc brashly taking over one more country and likely to try more if not resisted. US defense spending shot back up to wartime levels (though far from the WWII peak) and stayed there.
China also viewed it as a feeler for aggression that would go further if not resisted. Both countries were overinterpreting local issues as global ones.
The dramatic reverses were all in the first year, followed by two years of stalemate before the armistice.
I believe the answer would be A. they gained increases economic independence by working in factories
