Which choice completes the text so that it conforms to the convention…

Source Texts

Text

All member nations of the North Atlantic Treaty Organization, or NATO—including Iceland, which joined in 1949; Hungary, which joined in 1999; and Bulgaria, which joined in ______ are committed to NATO's principle of collective defense, each member pledging to defend all others.

Which choice completes the text so that it conforms to the conventions of Standard English?

2004;

2004,

2004

2004—