The Equal Protection Clause of the Fourteenth Amendment (1868) had

it is possible in choice D that "And" connects The Equal Protection Clause of the Fourteenth Amendment (1868) had been originally adopted............ and ......... has expanded

Whatever be the other reasons, the A, C, D and E are prima facie wrong because of using the inappropriate past perfect tense – ‘had been”. We can see that there is no other past event coupled with this past perfect and therefore these choices are not correct. This leaves us with only B, which uses the correct tense, namely simple past, for an event that happened in

A) had been originally adopted in order that blacks in the post-Civil War South be given the full benefit of citizenship, but over the past century and a half they are expanding it to include --- In addition the wrong use of past perfect, ‘are expanding’ is also wrong since ‘are expanding’ is a simple present progressive; When we say ‘over the past century and a half’ we have to mark it with a present perfect ‘have been’. And then who is the doer of ‘are expanding’ is not clear.

B) was originally adopted to give blacks in the post-Civil War South the full benefit of citizenship, but over the past century and a half it has been expanded to include – correct choice. It refers to the protection clause
C) had been originally adopted to give blacks in the post-Civil War South the full benefit of citizenship, while over the past century and a half was expanding it to include—‘over’ implies from the start to this day; 'was expanding' is also wrong; who was expanding, no one knows
D) had been originally adopted to give blacks in the post-Civil War South the full benefit of citizenship, and over the past century and a half has expanded to include—the order itself ‘has expanded to include’ --- is illogical
E) had been originally adopted by giving blacks in the post-Civil War South the full benefit of citizenship, and over the past century and a half they have been expanding it to include – who are the ‘they’?
.

MAGOOSH Official Explanation:

Split #1: the mystery pronoun! In (A) & (E), the subject of the second verb (are expanding/have been expanding) is the pronoun “they.” This is a mystery pronoun: it has no valid antecedent. There is no one in the sentence who qualifies as the “they” to which this pronoun refers. The GMAT can’t stand mystery pronouns. (A) & (E) are wrong.

Split #2: the sentence sets up a contrast: original narrow focus of the amendment vs. later, a very wide applicability. A contrast word would work better here. The word “but” in (A) & (B) is very good. This is a funny split, because while “but” is preferable to “and”, the word “and” is not so wrong that we could eliminate those choices on this basis alone.

Split #3: infinitive of purpose. The phrasing “adopted to give” is grammatical correct and concise and powerful --- exactly what the GMAT loves. By contrast, the phrasing “adopted in order that black be given” --- wordy and indirect, what the GMAT doesn’t like: (A) is wrong. The phrasing “adopted by giving” changes the meaning to something quite different, so this doesn’t work for this sentence: (E) is wrong.

Split #4a: look at the tenses of the second verb:

(A) “they are expanding it” --- are they doing this right now? Use of the present progressive does not make sense. This is wrong.

(B) & (E) “has been expanding” ---- has been happening and is still happening: that’s correct.

(C) “was expanding” --- did it stop? That’s not the right meaning. This is wrong.

(D) “has expanded” --- past but still going on: that’s correct.

On the basis of this split, we can eliminate (A) & (C). Now, given that the correct tense would be that of either (B) or (D) or (E), we can proceed on to:

Split #4b: the opening split, “was adopted” (simple past) in (B) vs. “had been adopted” (past perfect) in the other four. We need the past perfect when we are showing that some event happened earlier than some other past event. The past perfect tense establishes a contrast with the simple past. Here, though, the other verb, from (B) or (D) or (E), is going to be either “has been expanding” or “has expanded”, both present tense verbs. (Technically, “has been expanding” is the present perfect progressive, and “has expanded” is the present perfect.) Both of these are fundamentally based in the present tense, so all we need is the simple past tense. The past perfect is unnecessary and, in fact, incorrect in this context. (B) is the only choice.

For all these reasons, (B) is the best answer.

The sentence states that an amendment was adopted to achieve a specific purpose, essentially.

The Equal Protection Clause of the Fourteenth Amendment (1868) had been originally adopted in order that blacks in the post-Civil War South be given the full benefit of citizenship, but over the past century and a half they are expanding it to include all categories of civil rights.

A is incorrect because the first clause doesn't convey the full intention of the adoption in a grammatically correct manner. X was adopted TO achieve Y
In addition, "they" has no clear referent.

B) was originally adopted to give blacks in the post-Civil War South the full benefit of citizenship, but over the past century and a half it has been expanded to include
B is correct because it clearly and grammatically states the intention of the adoption, then a second independent clause is correctly connected via "[,]+ [FANBOYS]" structure

C) had been originally adopted to give blacks in the post-Civil War South the full benefit of citizenship, while over the past century and a half was expanding it to include
C confuses the tenses, incorrectly, by stating that the adoption occurred while the expansion was occuring.
"was expanding" has no clear reference either. Who was expanding?

D) had been originally adopted to give blacks in the post-Civil War South the full benefit of citizenship, and over the past century and a half has expanded to include
D incorrectly joins the dependent clause with a comma. There is no need for this.
Plus we should prefer the independent clause in B to D

E) had been originally adopted by giving blacks in the post-Civil War South the full benefit of citizenship, and over the past century and a half they have been expanding it to include
the first clause in E communicates that the amendment was adopted by DOING X (giving blacks in the post civil war south,...), which is obviously miscommunicating the logical meaning.
Again, "they" is incorrect

why aren't we considering the ambiguity of "it" here thoroughly. "it" can refer to a lot of things(ex : citizenship) and still be grammatically correct

Hello vishalsinghvs08,

We hope this finds you well.

To answer your query, in order for pronoun ambiguity to be applicable, the sentence must include multiple referents that make grammatical and logical sense for the pronoun.

We hope this helps.
All the best!
Experts' Global Team