Final answer:
The correct main heading to list in an index is 'D. Cookies,' as this is the broad category that would encompass all specific types and related topics as subheadings.
Step-by-step explanation:
When creating an index for a book or document, the main heading should reflect the most general or comprehensive category that encompasses all the subtopics or items listed beneath it. In this case, the potential headings are specific types of cookies or aspects related to cookies. The correct main heading to use in this context is D. Cookies, as it is the broad category under which the other items like Chocolate Chip, Oatmeal Raisin, and Dough, Storing Of would fall as subheadings or topics related to the main heading. This reflects the overall topic of the index and provides a clear organizational structure for readers.
In an index, the main heading should represent the overall topic or category that the entries fall under. In this case, the other options are specific types of cookies, but 'Dough, Storing Of' is a broader category that encompasses various aspects of cookie dough handling and storage.