Former communist nations began to join the european union in
a.2000
b.2002
c.2004
d.2006

The correct answer is C.

In 2004 ten countries joined the European Union: Cyprus, Czech Republic, Estonia, Hungary, Latvia, Lithuania, Malta, Poland, Slovakia and Slovenia.  Some of these countries, such as Latvia or Lithuania were formerly communist nations, which also were under the influence of the URSS during the Cold War era. It was the first time that former communist countries were accepted in the EU.

to extend a country’s power and influence