Answer:
Years in which the sources were published.
Explanation:
When you are doing academic work, you need to reference all the research sources you use in your work.
The part of the bibliographical references comes soon after completion, it is the first post-textual element. In it the author must list all the authors read and their respective works and works, addresses of websites, magazines, collections that were used to substantiate the work or to add content to the same. It is a very important part, so we must redouble our attention to avoid errors in the names of authors, works, year of publication or any element in the references. Not doing this part is virtually guaranteeing a zero score. Noting all the references used for the job as soon as they are consulted is the best way to ensure that none of them will be forgotten or lost.
It is not important that you put in the bibliographical references important years in Mandela's life, or the restless years in the life of the author. In addition, there is another place for you to place the year you conducted the search and that place is not in the bibliographic references.