The journalistic practice of fabricating remarks after an interview an

Premises:

Journalists use their own words but print them with " " marks (which seems to show that the interviewee said those words) - People call this unfair misrepresentation.

However, people’s actual spoken remarks don't convery their ideas clearly. A skilled journalist can better convey them in his words.

So this practice (of Journalist's own words in " ") avoids the more serious misrepresentation that would occur if people’s exact words were quoted but their ideas only partially expressed

Conclusion: This practice (of Journalist's own words in " ") should be acceptable.­

The argument is flawed. Why?

(A) answering an exaggerated charge by undermining the personal authority of those who made that charge

Nobody's personal authority is being undermined. 

(B) claiming that the prestige of a profession provides ample grounds for dismissing criticisms of that profession

The author does not say that all journalists are super skilled and hence we should not doubt that they are able to better represent the ideas through their words. He doesn't say journalists shouldn't be questioned, that the prestige of their profession is such that we shouldn't question them etc. 
So he doesn't claim that the prestige of a profession provides ample grounds for dismissing criticisms of that profession.

(C) offering as an adequate defense of a practice an observation that discredits only one of several possible alternatives to that practice

A practice - Journalist's own words in " "
The author is defending this practice by saying that a possible alternative (people’s exact words were quoted) is a worse option - so he is discrediting an alternative. 
But there are several other alternatives to the practice e.g. the journalist could summarize and present to the interviewee and if the interviewee agrees to that, then he can print it etc. But these altermnatives the author doesn't consider. He considers only one alternative, discredits it and hence defends the practice used. 
Hence (C) is correct. 

(D) concluding that a practice is right on the grounds that it is necessary

Not correct. He doesn't say the practice is necessary. 

(E) using the opponent’s admission that a practice is sometimes appropriate as conclusive proof that that practice is never inappropriate

No such discussion. We are not given that the interviewees sometimes  find this practice appropriate.

Answer (C)

 

Understanding the argument - ­
The journalistic practice of fabricating remarks after an interview and printing them within quotation marks, as if they were the interviewee’s own words, has been decried as a form of unfair misrepresentation. - Background info. 

However, people’s actual spoken remarks rarely convey their ideas as clearly as does a distillation of those ideas crafted, after an interview, by a skilled writer. - Opinion. An analogy - the participants in the chef competition are asked to create a fresh fruit salad. One of them uses canned fruits and justifies his reasoning by saying they are much better than having no fruits. This kind of reasoning is flawed. It discredits one alternative, i.e., using no fruits, but it misses other possible alternative options, i.e., fresh fruits, a combination of fresh and canned fruits, and so on. Likewise, in this option, the author discredits one alternative, i.e., "actually spoken remarks rarely convey their ideas" (if we don't use the distillation of ideas by a skilled writer). Still, there could be other possible alternatives that he misses, such as paraphrasing with content (For example, if someone gives a lengthy answer in an interview, a journalist might paraphrase it to make it shorter and more direct, then confirm with the interviewee that the paraphrased version still accurately conveys their original intent.) or providing context for quotes (This refers to adding additional information or explanation around a direct quote to give the reader a fuller understanding of the circumstances or meaning of the quote).

Therefore, since this practice avoids the more serious misrepresentation that would occur if people’s exact words were quoted but their ideas only partially expressed, it is entirely defensible. - Conclusion. 

Which one of the following is a questionable technique used in the argument?

Option Elimination - 

(A) answering an exaggerated charge by undermining the personal authority of those who made that charge - "personal authority of those who made that charge" is out of scope. 

(B) claiming that the prestige of a profession provides ample grounds for dismissing criticisms of that profession - "the prestige of a profession" is not even cited. Out of scope. 

(C) offering as an adequate defense of a practice an observation that discredits only one of several possible alternatives to that practice - ok

(D) concluding that a practice is right on the grounds that it is necessary - the argument says the "practice is defensible" and not "a practice is right." Wrong. 

(E) using the opponent’s admission that a practice is sometimes appropriate as conclusive proof that that practice is never inappropriate - "opponent’s admission" is not even cited. Out of scope. ­