Final answer:
Approximately 75 percent of American adults work in food service at some point in their lives. Therefore, the correct option is D. 75 percent
Step-by-step explanation:
The approximate percentage of American adults who work in food service at some point in their lives is 75 percent (D). According to the information provided, the United States has shifted to a postindustrial service economy, with 18 percent of the workforce employed in services. This indicates that a significant portion of American adults have worked in the food service industry at some point. Therefore, option D is the most accurate answer.