My sister has . . . . . . . . H. B. A degree. A. a B. an C. the D. no article

The other options are incorrect because they are all articles. An article is a word that is used to modify a noun. The articles “a” and “an” are used before singular nouns that begin with a consonant sound, while the article “the” is used before singular nouns that begin with a vowel sound or a consonant sound that is pronounced as a vowel sound. In this case, the noun “degree” does not begin with a consonant sound, so it does not need an article.