Agree with A. I can't help but not answer Anandnk
Authority: In this context, "an authority" is a noun and refers to a person in command or a person wielding some power/influence
Authoritarian: adjective characterizing the concentration of power (as in a regime) to an elite group or individual
A) right syntax and logic here. The sentence means to say that Walter Cronkite, and no less an authority than him, has reported...
B) unappropriate usage of "nonetheless" which means "in spite of something". Constructed as such, the sentence erroneously means: Walter Cronkite has reported [...] in spite of being an authority
C) "nevertheless" is synonymous to "nonetheless". Again, its usage is wrong
D) wrong idiom usage. "no less... than..." is right idiom
E) this changes the whole meaning of the sentence and conveys the idea that there is some power other than Walter Cronkite who has reported...