Since 1989, after the Berlin Wall had been demolished, one of the most problematic ethnic groups in the reunified Germany, in cultural and economic assimilation terms, was the former East Germans, who have had to acclimate to an entirely different political system.

a) after the Berlin Wall had been demolished, one of the most problematic ethnic groups in the reunified German, in cultural and economic assimilation terms, was the former East Germans

b) after the Berlin Wall was demolished, one of the most problematic ethnic groups in the reunified Germany, in cultural terms as well as those of economic assimilation, were the former East Germans

c) when the Berlin Wall was demolished, one of the reunified Germany's most problematic ethnic groups, in terms of cultural and economic assimilation, was the former East Germans

d) when the Berlin Wall was demolished, one of the most problematic ethnic groups in the reunified Germany, in terms of cultural and economic assimilation, has been the former East Germans

e) after the Berlin Wall had been demolished, one of the most problematic ethnic groups in the reunified Germany, in both terms of cultural and economic assimilation, have been the former East Germans


OA is D

which is correct ? when it comes to identify a race ? We re talking about the entire East Germans ... have or has ?