SC ; Source MGMAT

[Vaibhav Sinha]

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

OA is D

Would love to hear some comments on it.

[Matt P]

Looking at the original sentence, the two glaring parts are 'after the Berlin Wall' and 'were the former East Germans'. 'After' and 'were' do not fit will with 'Since 1989'. 

With a quick scan, we see after vs when, and based on this, (C/D) are superior to (A/B/E) assuming everything else fits.

Between C and D, we see that D corrects the 'were / has been' issue.

Reading D over, we confirm that the sentence is correct.