Answer:
D. Date/Time and Slide Number
Step-by-step explanation:
Headers and Footers allow you to add consistent elements which may or may not be auto genrated to the head (top) and/or foot (bottom) of your document.
These elements are seen on every page and they include: Page number, company logo, signature, date/time, slide number, references, author, page title, chapter, book title, etc.
Not all header elements can be auto generated, but slide number, time/date can easily be auto generated and is automatically added to every new page.
Headers and Footers are very important in formating text and organising documents, they also help in putting together references and table of content.
Other forms of headers and Footers exist in web development like HTML headers and Footers, which are quite similar to the ones in documents just that the are used in web pages. The information and contact details are placed at the bottom of the page is knoen as the footer while the header is usually the company logo and slogan with a background picture at the top.