I would call this the “ice age”
No, I would have not dropped the atomic bomb over Japan. The reason I state this is because I would have considered the many people that would have died in the act. Entire families would have been vanished or broken apart, many years would have been shed. A lot of hearts would have never been mended through the course of time, a horrid memory would have stayed with them till their very death. Also, many innocent people would pay for the act of a few bad men.
I would say the correct answer is D. Austria-Hungary would no longer exist if every ethnic group got its own independent territory.
As you can see, Austria-Hungary consisted of many ethnic groups at the time, including Germans, Poles, Slovenes, etc. What this meant for the nationalism is that each of these ethnic groups wanted their independence and to separate from Austria-Hungary. And if they did that, there would no longer be Austria-Hungary, but rather a bunch of new countries in Europe.