GMAT Sentence Correction (SC) | Re: The protest was effective, but not without cost: sixteen people died.

Let me clarify a few of these concerns:

*"But" is used as a conjunction here. There is no way to read this as a prepositional phrase.

*Many people will find the comma unnecessary here, but remember that while a comma can be a great structural clue, there aren't as many hard and fast comma rules as most people suspect. For instance, there are many cases in which the GMAT will separate subject and predicate with a comma (usually for clarity), even though that is frowned upon. That doesn't
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