Answer: I would contend that the right answer is the A) It is also delicious.
Explanation: Just to elaborate a little on the answer, it can also be added that although you have not provided the underlined portion of the sentence, it is possible to guess that the question is referring to the second part of it, when the student is describing fruit as "yummy." Since this letter is addressed to the principal of the school, the student should be using a formal and appropriate language, as he does in the first part of the sentence, employing words such as "nutritious" and "energizing." "Delicious" is a more appropriate option than "yummy." Replacing "yummy" for the other three alternatives would not be the best revision, since they all sound more informal.