Here is the argument in simple words:

First, you must understand what feudalism is. Here is an excerpt from the online dictionary:
Feudalism: A system of obligations that bound lords and their subjects in Europe during much of the Middle Ages. In theory, the king owned all or most of the land and gave it to his leading nobles in return for their loyalty and military service. The nobles in turn held land that peasants, including serfs, were allowed to farm in return for the peasants' labor and a portion of their produce. Under feudalism, people were born with a permanent position in society.
It is the legal and social system that evolved in W Europe in the 8th and 9th centuries, in which vassals were protected and maintained by their lords, usually through the granting of fiefs, and were required to serve under them in war...

Here is what the author tells you:

For writers who coined the term feudalism, existence of noble class was a must. Yet, the author says that legal sanction of status and inheritance of titles are a must to have a noble class. The author also says that feudalism existed in 8th century but inheritance of titles got legalized only in 12th century. The issue then is that how can "feudalism - the way it is defined" exist in 8th century if title inheritance was not legal at that time. So as far as actual history is concerned, existence of a nobility (status and title inheritance) cannot be necessary

Hence (A) makes complete sense.

(A) To say that feudalism by definition requires the existence of a nobility is to employ a definition that distorts history.

As for (C),
(C) The fact that a societal group has a distinct legal status is not in itself sufficient to allow that group to be properly considered a social class.

This cannot be inferred from the argument. The argument tells us that legal status is necessary to consider a societal group a social class. Whether it is sufficient or not, we do not know. Also, the argument only talks about the noble class; we don't know whether it holds for all social classes.
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OFFICIAL EXPLANATION

(A) Yes. According to the passage, feudalism existed in Europe from the eighth century to the twelfth century, which preceded the existence of a nobility. Hence, to say that feudalism requires the existence of a nobility contradicts history.

(B) No. This is the second-best choice. Choice (A) is better because it refers to the main idea of the passage that feudalism does not presuppose the existence of a noble class. Also choice (B) has a flaw in that we don’t know whether “dominant class” is synonymous with “noble class.”

(C) No. The opposite, however, is somewhat implied: The noble class was not deemed a social class until its titles were sanctioned by law.

(D) No. The passage implies that there was little or no cause and effect between nobility and feudalism.

(E) No. The passage implies that there was little or no cause and effect between nobility and feudalism.
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Three lines that helped me choose the right answer

-> the existence of feudalism presupposed the existence of a noble class
-> and there cannot be a noble class, unless both the titles and the inheritance of such titles are sanctioned by law
-> but the passage says feudalism already existed in eighth century ( Although feudalism existed in Europe as early as the eighth century) but inheritance of titles was not applicable till 12th century.

So the paradox is how can statement 1 and statement 3 be true at same time.

So Answer: A



kudos if this helped

Conclusion :

The coexistence of feudalism and noble class is NOT to be treated causal in nature. Law is required to sanction titles of nobility. However its not true that existence of feudalism required the existence of noble class.

B, D and E contradict the arg.

C has no bearing on the argument.

I pick E, but I think I understand why A is right now.

Argument:

History: Feudalism is in the same time with noble class, in 8th century.
Nobility, first appear in 12th century.

A - Nobility appear first Feudalism is wrong according to history ==> Like what the argument said

B - Dominant class could be king, knights... we don't know, so we can't say for sure feudaslim functioned without a dominant class -> WRONG

C - Societal group and social class were not discussed -> Out of scope -> WRONG

D - "The only cause" -> Too extreme, without proper evidence in the argument -> WRONG

E - Feudal institutions is a prerequisite of nobility -> sound like Feudal is a MUST for nobility to happen, there is no evidence in the argument suggest that -> WRONG

"Although feudalism existed in Europe as early as the eighth century, it was not until the twelfth century, when many feudal institutions were in decline, that the hereditary transfer of legally recognized titles of nobility first appeared."
so feudalism appears first and then comes the nobility titles and the reverse will be distort the history------>A
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I think I've seen this in the official guide. Brilliant question none the less.
The key to answering this was understanding the link between the premises. If you missed it, you're most likely picking B as I was tempted to do, before I gathered myself and re-read my notes.

Writers presupposed the existence of a noble class.
BUT, noble class cannot exist unless sanctioned by law.
Feudalism however, existed as early as 8th century, BUT was only recognised by 12th century.

Writers say for 'F' to exist, 'NC' must have always existed.
BUT 'F' existed by 8th century, and was only recognised by 12th century.

A - 'F' requires 'NC' to exist goes against history. KEEP.
B - dominant classes could have existed prior to 8th century, they just might not have been recognised. OUT. A is better.
C - Legal status is not equal to social class. Same as B really. OUT.
D - Only cause? This is over-stretching. OUT.
E - Existence of institution is neither under discussion, nor a necessity. OUT.

A wins!
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(A) To say that feudalism by definition requires the existence of a nobility is to employ a definition that distorts history.
Since the 8 th century we didn't have nobility doesn't rule out the complete existence of it hence it definitely distorts history

(B) Prior to the twelfth century, the institution of European feudalism functioned without the presence of a dominant class.
We cannot rule out the exisrtence of noble classes during the prexistence of feudalism

(C) The fact that a societal group has a distinct legal status is not in itself sufficient to allow that group to be properly considered a social class.
Here to we cannot determine whether nobility was one among social class or a higher class

(D) The decline of feudalism in Europe was the only cause of the rise of a European nobility.
We cannot fetermine this was the only cause one among many factors

(E) The prior existence of feudal institutions is a prerequisite for the emergence of a nobility, as defined in the strictest sense of the term.
First of all i eleminated above passage soley on the basis of strong language you can be assured Gmat won't employ such strong language from there on to the point we cannot determine whether it was sufficient condition or one among the conditions
Hence IMO E