Final answer:
There are 120 possible dinners with one appetizer, one main course, and one dessert.
Step-by-step explanation:
To find the number of possible dinners, we multiply the number of choices for each category.
There are 6 appetizers, 5 main courses, and 4 desserts. By the multiplication principle, the total number of possible dinners is 6 * 5 * 4 = 120.
Therefore, the correct answer is d. 120.