In search for further evidence to support B, I found these information in the
MGMAT SC book.
For your reference, the original problem and the first two alternatives are here:
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In good years, the patchwork of green fields that surround the San Joaquin Valley town bustles with farm workers, many of them in the area just for the season.
(a) surround the San Joaquin Valley town bustles with farm workers, many of them
(B) surrounds the San Joaquin Valley town bustles with farm workers, many of whom are
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I have 4th edition of the
MGMAT SC. On page 234, under "Modifiers: Exception to the Touch Rule"
1) A "mission-critical modifier falls between. This is modifier is often an Of-phrase that defines the noun. Example: He had a way OF DODGING OPPONENTS that impressed the scouts.
Without the Of-phrase, the sentence is meaningless.
In our problem, "patchwork" is meaningless without the of-phrase. So I would qualify this as a valid exception for the touch rule.
On page 236, under "subgroup modifiers"
Right: This model explains all known subatomic particles, SOME OF WHICH WERE only recently discovered
Wrong: This model explains all known subatomic particles, SOME OF WHICH only recently discovered
In other words, this construction requires a verb. As A lacks a verb, I would conclude this ungrammatical, a la
MGMAT.