Hi ran787, not sure if you read my post just above yours.

B uses for thwarting, whereas to thwart is preferable when intent needs to be depicted.

Also, B uses a comma before since, distorting the meaning.
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Hi Kunal, a run-on sentence is when two Independent clauses are connected by a comma. In both B and C, there is only one Independent clause:

Kudzu has overrun many houses and countless acres of roadside.

p.s. Our book EducationAisle Sentence Correction Nirvana discusses run-on sentence, its application and examples in significant detail. If someone is interested, PM me your email-id; I can mail the corresponding section.
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I believe "rampant" and "rampantly" change the meaning of the clause, but ultimate have the same effect.
"An Asian vine that has grown rampant" --> An Asian vine has become rampant. --> The vine is everywhere.
"An Asian vine that has grown rampantly" --> An Asian vine that has spread rapidly. --> The vine is everywhere.

(A)
"since introducing it..." looks like the start of a non-finite clause, which means that what we might be saying is "[An Asian vine] has grown rampantly in the southern United States since [the Asian vine was] introducing it in the 1920s to thwart soil erosion". The subject of our non-finite clause become "An Asian vine".
If we knew with 100% certainty that "since" was being used as a preposition here, then I think this option would be fine. But because we can't know with 100% certainty, this option can be misinterpreted.
Thus, we can rule this out

(B)
The comma makes the sentence much more ambiguous. We know that the "since" clause is a subordinate of "An Asian vine" clause, but our readers may not. With the comma, the "since" clause could potentially be mistaken as a subordinate of the main "Kudzu" clause. We don't need commas for subordinate clauses, so we might as well leave this one out as it makes the sentence clearer.
We can rule this out

(C)
Nothing wrong here

(D)
Same problem with (A)
We can rule this out

(E)
Same problem with (B)
We can rule this out

I think there is a run on sentence in option B

An Asian vine that has grown rampantly in the southern United States =>"Asian vine"is the subject and "has" is a verb and it expresses a complete thought.
Since it was introduced in the 1920 for thwarting soil erosion => "it" is the subject which refers to Kudzu and "was" is the verb and it also expresses a complete thought.

Even if we consider "Since" as a dependent marker and 2nd clause as dependent clause. What is the intent of the OG Explanations "The adverbial Clause Since it was introduced in the 1920 should not be set off from has grown rampantly"



Experts Please help. GMATNinja

As EducationAisle notes, there's no run-on in (B), because "that has grown rampantly in the southern United States" isn't independent - it's a modifier describing the Asian vine. Take a simple example: "Dan, who runs a mile in fifteen minutes, is not a great athlete." Here we do have two clauses, but the one in red functions as a modifier, and so it's not independent. In the OG question, "that has grown" is part of a modifier describing the vine. If there's only one independent clause, we don't have a run-on.

There are two ways to understand the OG's point. First, if we have a long modifier, and within this modifier we get additional information about when an action takes place, we typically won't use a comma between action and time-modifier.

For example, "My child, who has been screaming since she awoke at 3AM, supposedly has many positive qualities." Notice that the blue component is one long modifier describing "my child," and there's no need, within the modifier, to separate the action ("has been screaming") from the description of when the action takes place ("since she awoke"). Similarly, in (C) "that has grown rampant in the southern United States since it was introduced in the 1920s to thwart soil erosion" is one long essential modifier describing the "Asian vine." "Since it was introduced" tells us when the rampant growth started.

Second, the word "since" is tricky because it has two meanings. In both the official question and in my example above, it means "from the time when." But it can also mean "because."

Watch what happens if I insert a comma before "since" in the previous example: "...who has been screaming, since she awoke at 3AM." Now it sounds as though the kid has been screaming because she awoke at 3AM, rather than indicating the timeframe of her meltdown. The same thing happens in (B): "that has grown rampantly in the southern United States, since it was introduced in the 1920s." The growth happened because it was introduced in the 1920's? It makes sense to say that the 1920's marks the time when growth became rampant; it makes less sense to claim that the plant has grown wildly because it was introduced in this decade. So the version without the comma is more logical.

I hope that helps!
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