In Eastern Europe, Czechoslovakia split peacefully into two, forming two independent countries. Which two countries were they?

None of the above

In Eastern Europe Czechoslovakia split peacefully into two, with the Czechs and the Slovaks forming independent countries.

Czechoslovakia separated peacefully into two new countries, the Czech Republic and Slovakia (which is nowhere in the options)  so, 'D - None of the above' is the correct answer.

But the most severe conflict took place in the Balkan republics of Yugoslavia. After 1991, it broke apart with several provinces like Croatia, Slovenia, and Bosnia and Herzegovina declaring independence. Ethnic Serbs opposed this and a massacre of non-Serb Bosnians followed. The NATO intervention and the bombing of Yugoslavia followed the inter-ethnic civil war.