potential errors of manhattan sc guide

[gmatkiller_24]

I recently went through some key points and examples in the Manhattan Sentence Correction Guide. But When I read an example given in the Chapter 10 "Meaning, Structure & Modifier: Extra", in the Subgroup Modifier portion, I got confused by the example#4:

The first three examples are pretty straight-forward.
1. This model explains all known subatomic particles, some of which were only recently discovered.
2. This model explains all known subatomic particles, some of them only recently discovered.
3. This model explains all known subatomic particles, some only recently discovered.

But here is my confusion about the example 4:
4.This model explains all known subatomic particles, of which some were only recently discovered. （×）

The explanation given is : Notice that only the which construction has a working verb (were) in it. In contrast, wrong answer choices often include the following three incorrect constructions, which scramble the correct forms:

In terms of pure grammar, I cannot find any error in example#4. As you can see, there is indeed a verb "were" in the sentence.
If I were required to really find an disadvantage about example#4, I would only have to say that example# 1 is much more straight forward than example #4 in terms of structure, but both are fine in terms of pure grammar.

There are several officially correct answer using the "preposition + which" structure:
1. Like human DNA, the DNA of grape plants contains sites in which certain unique sequences of nucleotides are repeated over and over.
2. The Achaemenid Empire of Persia reached the Indus Valley in the fifth century B.C., bringing with it the Aramaic script, from which derive both the northern and the southern Indian alphabets

Please shed some lights on this issue. Thanks
BTW, Manhattan SC guide is really a great review material!

[StaceyKoprince]

Thanks for your questions. Please remember to read (and follow!) the forum guidelines before posting. This folder is only for general strategy questions, not content or specific test problems. Check out the content / problem folders and post in the relevant folder depending upon the source of the problem you want to post (and make sure to follow the rules about banned sources).

I will give you a short answer here, but if you would like to discuss further, please post in the relevant folder.

The preposition + which structure is an acceptable structure generally (as long as you follow certain rules). The lesson you are citing in the book, though, is talking specifically about using the word some in these constructions.

Here's an example of correct usage:
I have three cats, of which two are black.
--> If the preposition + which structure is used correctly, then you should be able to write the following sentence:
Two (of the three cats) are black.
In this sentence, the subject and verb are taken from the "of which" modifier. And the "of" is paired with the noun before the "of" to become a prepositional phrase in the sentence (this phrase can then appear after the subject or elsewhere in the sentence).

You can also do this with the two sentences you cited:
Certain sequences of nucleotides in (these) sites are repeated over and over.
The northern and southern Indian alphabets derive from the Aramaic script.

And then there's this weird thing with the word "some":
I like her cats, some of which are black. (Meaning: I like her cats and some of her cats are black.)
I like her cats, of which some are black. (Should be the same, right? It follows the same rule: Some of her cats are black.)

The second construction is considered awkward. Why? I don't know. But in general, it's considered better to use some of which than of which some.

Having said all of that: This is a very nitpicky issue and it's unlikely that you'll see any questions that specifically pair the word some with this construction. The broader usage (preposition + relative pronoun) is much more applicable / likely to be seen, so just know how to use this stuff properly (ie, the way that I described above—how you should be able to write a second sentence a certain way if the preposition + relative pronoun part is constructed correctly).