Contrary to popular belief, video games aren't just for killing an idle Thursday evening, in fact, a variety of recent studies have begun to demonstrate their teaching potential.


A. video games aren't just for killing an idle Thursday evening, in fact, a variety of recent studies have begun to demonstrate

B. video games aren't just to kill an idle Thursday evening, but a variety of recent studies, in fact, have begun to demonstrate

C. video games aren't just for killing an idle Thursday evening; in fact, a variety of recent studies has begun to demonstrate

D. video games aren't just for killing an idle Thursday evening; in fact, a variety of recent studies have begun to demonstrate

E. video games aren't just for killing an idle Thursday evening, and a variety of recent studies have begun in demonstration of

Contrary to popular belief, video games aren‘t just for killing an idle Thursday evening, in fact, a variety of recent studies have begun to demonstrate their teaching potential.

A. video games aren‘t just for killing an idle Thursday evening, in fact, a variety
of recent studies have begun to demonstrate

B. video games aren‘t just to kill an idle Thursday evening, but a variety of
recent studies, in fact, have begun to demonstrate

C. video games aren‘t just for killing an idle Thursday evening; in fact, a variety
of recent studies has begun to demonstrate

D. video games aren‘t just for killing an idle Thursday evening; in fact, a
variety of recent studies have begun to demonstrate

E. video games aren‘t just for killing an idle Thursday evening, and a variety of
recent studies have begun in demonstration of

Clauses are "dependent" or "independent" only based on the presence of a main subject and main verb. Here we have "games aren't," a subject and a verb, neither one subordinated by a relative pronoun, preposition, or subordinating conjunction, so they are a Main Subject and a Main Verb. Later, we have "variety ... has begun," another subject and verb, again Main Subject & Verb because they are not subordinated. Two independent clauses require either a semicolon or a coordinating conjunction (FANBOYS).

Furthermore, the verb cannot be "have" in the second clause; the subject is "variety." Remember, anything following a preposition, such as "of," is NEVER the main subject of anything. "recent studies" is the object of "of," not the subject of "have begun."

In terms of pronouns, pronoun ambiguity only has to do with whether or not there is one clear logical antecedent, agreeing in number with the pronoun. An ambiguous pronoun does not make a sentence "dependent." Take, for example, the following paragraph:

"I am really happy with my GMAT tutor. He is professional and knowledgeable and on time and knows a lot about the test. I am thankful for this, because it is a difficult test."

All three sentences are clearly complete sentences and fully independent clauses. "He" in the second sentence refers to "tutor," and "it" in the third refers to "test." Obviously on the GMAT this never happens, since Sentence Correction only tests single sentences. However, the moral of the story is that, in English grammar, pronouns do not have to have their antecedents in the same sentence or clause.
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I don't this is a valid question , because the difference between A and D is only the punctuation, GMAT would never differentiate between two sentences based JUST on punctuation.

Snippet from article published here http://online.wsj.com/public/resources/ ... S.0706.pdf.

The stylebook’s entry on collective nouns
advises that with words such as variety, number
and total, a rule of thumb is to use a singular
verb when the article the precedes the noun
and a plural verb when the article a is used.

Understand what mentioned above in conjunction with explanation by Adam in above comments.

A variety of bird is very popular (correct)
A variety of birds are in our building (correct)
The variety in languages is rare. (correct)

So there was something more left to learn besides "a number of".
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Our greatest weakness lies in giving up. The most certain way to succeed is to try just one more time. ― Thomas A. Edison
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Yes, "Variety" similar to "bunch" and "a number" => A collection of distinct items.

"A number" is plural. "The number" is singular.

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