Question

as a result of an agreement signed by great britain and ireland in 1998, northern ireland
became an independent country.
joined with southern ireland.
gained the right to choose its own future.
became a part of great britain.

Explanation:

The 1998 Good Friday Agreement (signed by Great Britain and Ireland) established that Northern Ireland's status could be changed if a majority of its population votes for unification with the Republic of Ireland, giving it the right to determine its own future. It did not make it independent, merge it immediately with Southern Ireland, or make it part of Great Britain (it was already part of the UK, which includes Great Britain and Northern Ireland).

Answer:

gained the right to choose its own future.