C. His hours are long and busy.
Linking verbs are do not express action. It simply links the subject of the verb to the additional information about the subject.
In the above sentence, ARE is the linking verb. It does not express any action. Its subject is his hours. It connects the additional information long and busy to the subject his hours.
Verbs in other choices pays, works, and has walked are all action verbs. It does not connect the subject to additional information about the subject. Instead, the verb shows the subject doing the action (he works, he has walked) or the subject receiving the action (his boss pays him).
