Final answer:
The sentence with the abstract noun is 'D. Respect must be earned,' where 'respect' is the abstract noun. It represents a concept, not a concrete object. Other sentences provided need punctuation revisions for clarity.
Step-by-step explanation:
The sentence that contains an abstract noun is option D: Respect must be earned. An abstract noun is a noun that represents something that cannot be touched, such as a feeling or concept. In this case, the noun 'respect' represents a concept or quality, making it an abstract noun.