Bunuel
In 1983, using both ground-penetrating radar equipment—much of it constructed themselves—as well as clues from the autobiography of film director Cecil B. DeMille, the film enthusiasts Peter Brosnan and John Parker located and unearthed the massive set of DeMille's epic 1923 film The Ten Commandments.
(A) much of it constructed themselves—as well as clues from the autobiography of film director Cecil B. DeMille, the film enthusiasts Peter Brosnan and John Parker
(B) they constructed much of it themselves, and used clues from film director Cecil B. DeMille's autobiography—Peter Brosnan and John Parker, the film enthusiasts,
(C) constructing much of it themselves—and taking clues from film director Cecil B. DeMille's autobiography, Peter Brosnan and John Parker were film enthusiasts who
(D) they constructed much of it themselves, as well as clues from film director Cecil B. DeMille's autobiography—Peter Brosnan and John Parker were film enthusiasts who
(E) much of which they constructed themselves—and clues from the autobiography of film director Cecil B. DeMille, film enthusiasts Peter Brosnan and John Parker
OFFICIAL EXPLANATION
According to this sentence, Brosnan and Parker used two things in finding the set of The Ten Commandments: radar equipment and clues from DeMille's autobiography. The sentence also notes that the two film buffs built much of the radar equipment themselves. The dashes set off text to convey an interesting detail that is only tangentially relevant to the core of the sentence.
(A) The structure both X as well as Y is unidiomatic; the correct idiom is both X and Y. Themselves modifies constructed, which in turn modifies equipment; the construction thus implies that themselves refers to the equipment; this is not only illogical but also ungrammatical, as themselves is plural and equipment is singular.
(B) If the section between dashes is removed, the remaining construction contains the first half of an idiomatic construction (both X), but not the second half (and Y). This is not acceptable; both halves should be together between the dashes OR together outside of the dashes. Further, the sentence loses meaning by placing used clues inside the dashes. They used equipment to locate the film set; as an aside, they constructed much of the equipment themselves and they used clues. What did they use the clues to do? The sentence doesn't say.
(C) In the construction both ground-penetrating radar equipment and taking clues, equipment and taking are not parallel. The core sentence reads: using radar equipment, Brosnan and Parker were film enthusiasts who located the set of the film. The two did not use the radar equipment to be film enthusiasts; rather, they used the radar equipment to locate the film set. The meaning is illogical.
(D) The structure both X as well as Y is unidiomatic; the correct idiom is both X and Y. If the section between dashes is removed, the remaining construction contains the first half of an idiomatic construction (both X), but not the second half (and Y). This is not acceptable; both halves should be together between the dashes OR together outside of the dashes. Further, the choice appears to say that they constructed the equipment and the clues. Finally, in the construction both ground-penetrating radar equipment and taking clues, equipment and taking are not parallel. The core sentence reads: using radar equipment, Brosnan and Parker were film enthusiasts who located the set of the film. The two did not use the radar equipment to be film enthusiasts; rather, they used the radar equipment to locate the film set. The meaning is illogical.
(E) CORRECT. Much of which properly refers to radar equipment, and they and themselves point to Brosnan and Parker, who are mentioned later in the sentence. The sentence core, using radar equipment, Brosnan and Parker located the set of the film, is logical.