Below is a relatively difficult GMAT sentence correction. A couple of concepts are being tested, so proceed cautiously. A detailed explanation follows.
Despite the curator’s claim, none of the unattributed sketches in the museum’s upcoming Flemish exhibit, all estimated to be more than 400-years old, are likely the work of Jan Vermeer, who was active in Flanders during the 17th Century.
(A) to be more than 400-years old, are
(B) to be over 400-years old, is
(C) at over 400-years old, are
(D) at more than 400-years old, is
(E) to be older than 400-years, is
A good approach is to notice the 3:2 split between is and are at the end of each answer choice. So which is it? Well, if we look at the subject we see we are dealing with “none of the attributed sketches.”
Whenever you see ‘none’ look to the subject after the preposition, in this case sketches. Sketches is plural – we want the verb ‘are.’ Eliminate (B), (D) and (E).
Answer choice (C) uses the improper idiomatic construction estimated at. It should be estimated to be. And don’t pick (C) simply because it is the shortest. Concision at the expense of grammar is never a good idea.
(A) contains the proper idiomatic construction, estimated to be, and the correct subject-verb agreement, none…are.