The correct answer is D. am.
The pronoun “I” is always capitalized because it is a subject pronoun. Subject pronouns are used to refer to the person or people who are doing or being something. In the sentence “I am always capital,” the pronoun “I” is the subject of the sentence. The verb “am” agrees with the subject “I” in number and person.
The other options are incorrect because they are not subject pronouns. The verb “do” is a main verb, the verb “is” is a linking verb, and the verb “has” is a helping verb. Main verbs are used to express the action of a sentence. Linking verbs are used to connect the subject of a sentence to its predicate. Helping verbs are used to help main verbs express tense, aspect, or mood.
In the sentence “I am always capital,” the verb “am” is a linking verb. It connects the subject “I” to the predicate “always capital.” The predicate “always capital” tells us something about the subject “I.” In this case, it tells us that the subject is always capital.