How Has North Korea Managed to Survive Up Until Now

How has North Korea managed to survive up until now?

A) The prison camps output massive amounts of food, more than enough to feed themselves and a few other countries if they needed to.
B) Other countries, afraid of their nuclear threats, offer them supplies to appease them.
C) By begging for "talks," fuel, and food in exchange for behaving themselves.
D) North Korea clearly does have a magical machine with unknown properties but it seems to output resources.