The correct answer is (D) no article.
The word “cadet” is a common noun, which means that it does not refer to a specific person or thing. In this case, the speaker is not referring to a particular N.C.C. cadet, but rather to N.C.C. cadets in general. Therefore, the article “a” or “an” is not necessary.
The article “the” is used to refer to a specific person or thing that has already been mentioned or is known to the listener. In this case, the speaker has not mentioned any specific N.C.C. cadet, so the article “the” is not appropriate.
The article “a” or “an” is used to refer to a general person or thing that is not specific. In this case, the speaker is referring to N.C.C. cadets in general, so the article “a” or “an” is not appropriate.