Whereas – is a comparison marker that usually compares two clauses, or to be more precise, the subject of the first clause with the subject of the second clause. Accordingly, subjects of both clauses must be parallel to one another. Since American dialects is the subject of the first clause in the non-underlined part of the sentence, the subject of the second clause must be European dialects.
Structure: Whereas American dialects (subjet) adopt..., European dialects (subject) tend...
The above is the correct structure comparing parallel subjects. With that in mind, let’ analyze the below answer choices.
A. Whereas American dialects of the English language often adopt words from other languages, those of European dialects tend...
The green parts above are parallel to one another but whereas is not comparing them, because European dialects is not the subject but the object of the second clause. Whereas can’t compare the subject to the object. What whereas is incorrectly comparing here are American dialects and those. Those may refer to languages, words, or American dialects. In any case the comparison becomes nonsensical:
Whereas American dialects adopt…, languages of European dialects tend… here dialects is not parallel to languages
Whereas American dialects adopt…, words of European dialects tend… here dialects is not parallel to words
Whereas American dialects adopt…, American dialects of European dialects tend… nonsensical and not-intended meaning.
B. Whereas American dialects of the English language often adopt words from other languages, that of European dialects tends...
Like A, B incorrectly tries to compare the subject of the first clause with the object of the second clause. What whereas is incorrectly comparing here are American dialects and that. The only singular noun that may refer to is English language:
Whereas American dialects adopt…, English language of European dialects tends… here dialects is not parallel to English language, so the comparison is nonsensical.
C. Whereas American dialects of the language of English often adopts words from other languages, that of European dialects tends...
Like A and B, C incorrectly tries to compare the subject of the first clause to the object of the second clause. As in B, what whereas is incorrectly comparing here are American dialects and that. The only singular noun that may refer to is language of English:
Whereas American dialects adopts…, language of English of European dialects tends… here dialects is not parallel to language of English, so the comparison is nonsensical.
Additionally, American dialects adopts is a subject-verb disagreement.
D. Whereas American dialects of the English language often adopts words from other languages, European dialects tend...
Finally, the sentence has a correct parallelism. However, as in C, American dialects adopts is a subject-verb disagreement.
E. Whereas American dialects of the English language often adopt words from other languages, European dialects tend...
Whereas correctly compares American dialects with European dialects. There is no subject-verb disagreement. E is a correct sentence.
Hence E