His tour of the new outdoor mall, erected in the newly revitalized

Another point is that you cannot use "when'". "When" can only be used in case of time.

Option C leads to the following phrase:

... an America when segregation had existed in current multi-ethnic areas

1. As ArupRS mentioned, we'd normally use a when for a time or an era, but this option puts it right next to America. This makes in which a much better option than when in this question.

2. As rakeshtewatia0105 pointed out, there is no need to shift to the past perfect in the description of an America because there is nothing else in the description for which the sequence needs to be clarified. For example:

That was the time when we met them.
That was the time when we had met them.

3. The adjective current is incorrect. We need the adverb currently.

Do you want the current empty house?
This means that the house is current.

Do you want the currently empty house?
This means that the house is currently empty.

Similarly, we should go with what are now or currently, not with current. Keep in mind that putting both now and currently together (A) would be redundant.

Also, if anyone is interested, this question is based on this official question. You may want to attempt that question as well.

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