Step-by-step explanation:
In English, "smoking" is a gerund in grammar. Therefore, the correct answer is (D) Gerund. Gerunds are verb forms that function as nouns, and they are formed by adding -ing to the base form of a verb. In the case of "smoking," it functions as a noun and can be the subject, object, or complement of a sentence. For example, "Smoking is harmful to your health" or "I enjoy smoking."