Political scientist: It is not uncommon for a politician to criticize

I will state E. D is tempting but that part of the passage seems to be context for the larger point that is E.

I still have problems determining conclusions, so here I am not sure whether the conclusion is that such criticism is insincere or that mentioned agendas won't be realized ("I am more on the won't be realized" side though)
Here A, B, and D all use "sincere" to link some other staff, as per my understanding
I didn't fully understand C, but I think we can infer nothing about ineffectiveness
However, even though E restates the last sentence (which, in my opinion, is a conclusion), it doesn't involve info from other sentences, and what I learned from CR Bible is that it should.

The answer is D. Here is my 2 cents

The political scientist first describes how generally the politicians criticize their opponents for presenting ideas in a way that cannot be understood. The "however" in the second sentence indicates that the political scientist disagrees with this criticism—specifically, he claims that it is never sincere.

A) This answer choice indicates that the politicians' opponents should be considered insincere. The main conclusion is that the politicians' criticism is insincere.

B) The political scientist doesn't claim that politicians are insincere whenever they criticize the manner in which an agenda is presented. The conclusion is only about criticism that focuses on one specific manner of presenting an agenda: presenting it in an incomprehensible way.

C) The conclusion is that a certain type of criticism is never sincere, but the political scientist doesn't actually say that this is a reason to refrain from that criticism. Refraining from criticism, or engaging in it, is an entirely new concept that isn't part of the main conclusion.

D) This is the political scientist's conclusion.

E) This connects two ideas in the last sentence of the stimulus, but it's not something explicitly stated in the stimulus and is not the main conclusion.

Political scientist: It is not uncommon for a politician to criticize his or her political opponents by claiming that their exposition of their ideas is muddled and incomprehensible. Such criticism, however, is never sincere. Political agendas promoted in a manner that cannot be understood by large numbers of people will not be realized for, as every politician knows, political mobilization requires commonality of purpose.

Which one of the following is the most accurate rendering of the political scientist’s main conclusion?

(A) People who promote political agendas in an incomprehensible manner should be regarded as insincere. - WRONG. Not necessarily true. But most importantly it's an inference.

(B) Sincere critics of the proponents of a political agenda should not focus their criticisms on the manner in which that agenda is promoted. - WRONG. It is not about the way such criticisms are made.

(C) The ineffectiveness of a confusingly promoted political agenda is a reason for refraining from, rather than engaging in, criticism of those who are promoting it. - WRONG. Makes an inference which is wrong.

(D) A politician criticizing his or her political opponents for presenting their political agendas in an incomprehensible manner is being insincere. - CORRECT. ''Being insincere' equates to 'never sincere'.

(E) To mobilize large numbers of people in support of a political agenda, that political agenda must be presented in such a way that it cannot be misunderstood - WRONG. Too good to be true was my initial thought and i fell for it. This at best can be an inference than something that equates to conclusion.

Answer D.
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