The two essential parts of the sentence are the - subject and noun - adjective and verb - subject ad verb

The correct answer is:  [C]:  "subject and verb" .

   The two essential parts of [the sentence] are the "subject and the verb". 

    NOTE:  This is assumng that, among the 3 (THREE) answer choices given, the third option meant to be:  "subject and verb" ; and that the word: "ad" ; was merely a spelling error—or "typographical error"—that was supposed to be:  "and" .   We futher confirm such an assumption based on the folllowing:  
1)  that the first 2 (TWO) answer choice are incorrect;  2)  that:  "subject and verb" ; would be a correct answer; 3)  that there are only 3 (THREE) answer choices provided; 4)  that the third answer choice:  "subject ad {sic} verb" ; resembles "subject and verb" very closely; and 5)  that there are no answer choices such as: "all of the above"; "none of the above"; or "the first and the third options are correct"