Re: Since 1989, after the Berlin Wall had been demolished, one

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, were the former
East Germans, who have had to acclimate to an entirely different political system.

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


We have to use past perfect tense with "since" so A, B, C can be ruled out.
E is worng, because "have" does not agree with one of the most problematic ethnic group n numbers.
We are talking about one group only, so has should be used.

So we are left with the correct option: D