Read each sentence to find out whether there is any grammatical error in it. The error, if any will be in one part of the sentence. The letter of that part is the answer. If there is no error, the answer is 'D'. (Ignore the errors of punctuation, if any). (solve as per the direction given)

The sentence reads: "Since it was his first election campaign, the candidate was confused; none could clearly understand either the principles he stood for or the benefits he promised." Let's break it down to identify any grammatical error:

1. Option A - Since it was his first election campaign, the candidate was confused:
   • This part is grammatically correct. The sentence begins with a correct causal structure "Since it was his first election campaign" and the main clause "the candidate was confused" is also fine.


2. Option B - none could clearly understand:
   • This part is also correct. The use of "none" as the subject is grammatically fine here, and the sentence is clear and structurally correct.


3. Option C - either the principles he stood for or the benefits he promised:
   • This is where the error lies. When using "either... or" in a sentence, the verb that follows should agree with the noun closer to it. Since "principles" is plural, the verb should be "could clearly understand" and should be followed by "either the principles he stood for or the benefits he promised," which is grammatically correct.
   
   
   • The phrase "either the principles he stood for or the benefits he promised" should correctly be "either the principles he stood for or the benefits he promised" without changing the verb.


4. Option D - No error:
   • There is an error in Option C with the structure of "either... or," but the rest of the sentence is correct.


5. Final Answer:
   • The error is in Option C. The correct answer is C.