Hi sinsofgmat,

Beyond the standard grammar rules that the GMAT will test you on (verbs, pronouns, parallelism, etc.), the GMAT will also test you on a variety of grammar rules involving idioms, style and proper usage. Some of the wrong answers will be written in a way that is similar to how people talk (it's commonly referred to as "conversational language", but it's almost never grammatically correct), so you have to be very careful about knowing the rules and relying on those rules to dictate which answer you choose.

Here, the word "seem" (which appears right before the underlined portion of the sentence) triggers a phrase that must come next.

The most common phrase that I can think of that uses the word "seem" is "seem to be...." (or "seems to be"); you'll notice that the word "seem" is followed by an infinitive (in this example, it's "...to be"). This is a grammar rule, so we have to follow it. The only answer that follows this rule is the correct one.

Final Answer: C

While I imagine the OG explanation probably went into some detail about the various reasons why the wrong answers were wrong, the short answer is that they don't use an infinitive, so they're incorrect.

GMAT assassins aren't born, they're made,
Rich