What was the “velvet divorce”?
czechoslovakia’s split into two countries
the rift between czechoslovakia and poland
the end of communism in czechoslovakia
the first phase of the velvet revolution

Czechoslovakia's split into two countries

Explanation:

The Velvet Divorce is a term used for the split of Czechoslovakia into two separate countries. The separation was peaceful, without violence, so it was all negotiated without any problems, with the two newly formed nations remaining in good relations. The reasons for the split were that the two parts of Czechoslovakia had different political aspirations, had different ethnic groups, and they had different opinions as two how they should develop. It is an interesting case among the Slavic nations though, as in most cases there has always been lot of bloodshed, while in this case it was all peaceful and calm.

a and b because with the other three, they simplify to something else.

the mediterranean sea