Hello, wali786 and Ritesh92gmat. A run-on sentence occurs most commonly when an independent clause follows a conjunction, but there is no comma before the conjunction. However, the run-on in (E) is of a different nature:


The that clause is incorrectly embedded within the what clause instead of defining that what. To be clear, you can say, What astronomers have long believed is that..., but you cannot say, What astronomers have long believed that... Likewise, you could say, Astronomers have long believed that..., without the nominative what clause. Since the what clause in (E), right through the word believed, acts as a direct object, we need for that object to resolve before we start describing it in a namely way, the role that either a colon or an em dash can play in such a sentence. Without that crucial pause, the sentence becomes a run-on. Compare:

1) The what clause as a subject—What I said that he should tell the truth. (Missing verb.)
2) The what clause as an object—His version is different from what I said that he should tell the truth. (Missing pause.)

To refer back to what I said, I am using another clause, only one that begins with a that, and I need to make it clear that that second clause is defining or describing the first.

I hope that helps. This is a tricky question, one that has given me more grief than just about any other (if you look back through the history).

- Andrew

AndrewN
Hi Andrew, thanks for your reply.

"This is a tricky question, one that has given me more grief than just about any other (if you look back through the history)."

Agree , I saw the history but I should say that I really learned few important points from your replies.
So, many thanks to you again.

Hello, BlairS. I have discussed this query at length just two posts above, here. I hope the explanation helps.

- Andrew

AndrewN - thanks for the explanation in earlier posts. I tripped on with D using the same logic that colon and “that” together were creating a redundancy. Saw a post where you happen to mention an official question that uses the structure as is there in choice A.

Adding this to flash card as we speak!

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Yes, Ravi: that can appear after a colon. This does not mean that it always needs to appear when it could, just that its appearance does not create an automatic redundancy, as some earlier posts have claimed. In a sense, I wish this question would go away. But if the dialogue can apprise GMAT™ aspirants of even one lesser known exception to a general tendency, and such an exception has shown up in an official SC question, then perhaps my efforts have not been in vain.

Good luck with your studies.

- Andrew

Here's why A is better than D (or why I chose A): it's because the meaning is clearer in A. The sentence is easier to understand.

The THAT in A makes it clear that 'Astronomers have long believed THAT such bodies are...'. So the link between the first and second part of the sentence is made explicit; what we get after the colon is a statement of what astronomers have long believed.

Without the THAT, we would have an independent clause after the colon. Readers would have to take an extra mental step to understand the meaning.

Redundancy is about unnecessary (and usually illogical) repetition. When the addition of a word increases comprehensibility and makes reading more effortless, we do not consider the word redundant.


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