Official Explanation
(A)Although offering a dynamic range simply absent on the harpsichord, the original fortepiano, invented in the early eighteenth century
This is one of the classic mistakes on the GMAT Sentence Correction. A subordinating conjunction such as “although” must be followed by a bonafide noun-verb, not simply by a participle. Correct: “Although the original fortepiano offered etc.” Incorrect: “Although offering etc.” In addition to that mistake, notice that, after the first comma, we have the free-standing noun “the original fortepiano,” a subject without a verb. (A) has a few mistakes, so it is incorrect.
(B)Although the original fortepiano, invented in the early eighteenth century, offered a dynamic range simply absent on the harpsichord
This one correctly follows “Although” with a bonafide noun-verb clause. In fact, (B) is the correct answer.
(C)Although it offered a dynamic range simply absent on the harpsichord, the original fortepiano, invented in the early eighteenth century
This one correctly follows “Although” with a bonafide noun-verb clause, but then has the free-standing noun “the original fortepiano,” a subject without a verb. (C) is incorrect.
(D)Invented in the early eighteenth century, the original fortepiano offered a dynamic range simply absent on the harpsichord
This one begins with the statement “invented in the early eighteenth century”: this is a minor detail, tangential to the main point of the sentence, so it’s somewhat jarring as the opening of the sentence. The BIG problem with this one, though, is that we have an independent clause “the original pianoforte offered …” and then, after the dashed section, another independent clause “the fortepiano would now sound …” and there’s no conjunction. This is a run-on sentence, and therefore, (D) is incorrect.
(E)The original fortepiano, invented in the early eighteenth century, although it offered a dynamic range simply absent on the harpsichord
This one is strange. We get a subject, followed by a modifier and then a subordinate clause, but there’s no verb. We have a free-standing noun without a verb. This sentence has the form noun-noun-verb, not exactly a run-on, but still very much incorrect. (E) is incorrect.
Answer = B