Answer: What must follow the verbs "look", "sound", smell" and "stand" is D. an adjective.
Explanation: All of the verbs provided ("look", "sound", "smell" and "stand") are linking verbs. Linking verbs do not present an action. They actually establish a connection between the subject and another element in the sentence, an adjective, that provides information about that subject and describes it. Moreover, linking verbs are always followed by adjectives. Examples are the sentences "She looked tired" and "His mother sounded worried".
