Of the options given in this question, the best choice is B. B is already part way to having a command economy and is the situation where a command economy is most likely to occur.
A and C are the worst choices. There, the people have many contacts with outside lands. It will be much harder for the government to keep control over the economy in such a situation.
D is somewhat better. A government in such an area would have more control over its people. However, the fact that the economy is overwhelmingly agrarian makes it unlikely that a command economy will arise.
B is the best choice. The country is already at war, meaning that the government will be allowed a great deal of power. The government is already controlling the economy in significant ways such as rationing. The urban environment makes it easier for government to control the people. All of this makes B the best choice.