Bunuel
The vice-president of engineering argued that the biggest advantage of the proposed alloy for the designs of the new fuselage
would lay in not its unusually light weight but in its superior resistance to the corrosive influence of the elements.
(A) would lay in not its
(B) would lie not in its
(C) will lie in not their
(D) will lay not in its
(E) would lay in not their
Magoosh Official Explanation
Split #1: "would" vs. "will". The word "will" denotes the unambiguous factual future: "X will happen." The word "would" indicates the subjunctive, which signals a tentative prediction or hypothetical assertion: "X would happen." Which is correct here? Well, the new alloy is "proposed", so it may be tentative, or perhaps the proposal was fully approved already and the use of the alloy is not in doubt. We don't have enough information to decide between these two. We cannot eliminate answer choices based on this split.
Split #2: lie vs. lay. We are talking about the where the biggest advantage "is located" --- the verb that means "to be located" is "to lie." The word "to lay" is absolutely incorrect in this context, so choices (A) & (D) & (E) are all incorrect.
Split #3: the common word in parallelism. We are using the parallel structure not P but Q. Both P & Q are prepositional phrases in parallel, phrases following the preposition "in". Here, we need to follow the "once outside or twice inside" rule. We could either have the preposition "in" appear once, outside the parallel structure, applying equally to both terms --- in not P but Q --- or it could appear inside the parallel structure twice, once in front of each term --- not in P but in Q. Notice that the second part, after the underlined section, has the preposition: "in its superior resistance …" Therefore, "once outside" is not an option here: we must go with the "twice inside" plan. This means, in the underlined section, the word "in" must follow the word "not" --- only (B) & (D) get this correct, and the others must be incorrect because they have the wrong order.
Split #4: pronoun. What has the "unusually light weight"? Either the alloy, the physical material, or the fuselage, the physical product --- both are singular. The only plural noun is "designs" --- designs are ideas, so they don't have physical weight. The pronoun at the end of the underlined section must be the singular "its", not the plural "their." Choices (C) & (E) make this mistake and are incorrect.
For all these reasons, the only possible answer is (B).