gandalfthegreat
zhanbo,
I have great confidence in your answers as well, and following your posts and great explanations

However, I could not understand the explanation for how D and E are incorrect. Could you please explain what verb you mention is needed to rectify them, and clarify the “relative clause”?
Thanks!
Posted from my mobile device Hi,
gandalfthegreatThe relative clause (read more at
https://writingcenter.unc.edu/tips-and- ... e-clauses/) must be a clause: Every clause must have a verb (and virtually all clauses in GMAT also must have a subject).
In (E), we seem to have
one independent clause followed by
an unrestrictive relative clause.
A dozen luxury apartment building projects are being carried out in one particular stretch,
most of which begun only recently .
We think it is a relative clause because of the use of "most of which", in which "which" is the relative pronoun.
In the relative clause, its subject is "most of which" = "most of the luxury apartment building projects"
But there is no main verb for the subject.
We do see "begun", which is past participle of "begin". But we know that a past participle itself cannot be the main verb. (a past participle can pair with a helper verb such as "have / be" to constitute the main verb.)
So (E) fails to construct a valid relative clause. It can be fixed by adding "were" before "begun".
In (D), the relative clause ("which were begun only recently") is valid
*, and it modifies "most of them".
A dozen luxury apartment building projects are being carried out in one particular stretch, most of them
which were begun only recently.
But if we remove the relative clause, we get:
a dozen luxury apartment building projects are being carried out in one particular stretch,
most of themWe could not place the added phrase "most of them" after the comma with the rest of the sentence. Take a look at the following sentence:
We have to practice for GMAT tests, some of usIf you can see the issue with the sentence above, well, (E) suffers the same fatal error.
* Also, Take note that, as a restrictive relative clause, "that were begun only recently" should be used in the place of "which were begun only recently". This rule is not really honored in British English. In American English / GMAT, however, such a distinction matters.