Confused a little is verb correct in following sentence?
Not only the newspaper, but also the radio warns of the approaching crisis.
Yes, the verb is correct, but be sure to put a comma after "radio" for complete correctness.
http://grammar.ccc.commnet.edu/grammar/commas.htm
Scroll down and see #4.
Also this:
http://grammar.ccc.commnet.edu/grammar/conjunctions.htm#correlative_conjunctions
Yes, the verb "warns" is correct in the sentence you provided. The subject of the sentence is "the newspaper" and "the radio," which are considered as a compound subject because they are joined by the conjunction "not only...but also." This means that both the newspaper and the radio serve as subjects and should agree with the verb "warns."
To confirm this, you can ask yourself the question "What warns?" The answer would be "the newspaper and the radio." Therefore, the verb should be in the third-person singular form, which is "warns."