* Primary sources are original materials created during the time period being studied. They provide firsthand accounts and perspectives.
* Diary: A diary is a personal record of events, thoughts, and feelings written by the person experiencing them. This makes it a direct, firsthand account.
* History textbook: Textbooks are secondary sources. They compile and interpret information from primary sources.
* Biography: Biographies are also secondary sources. They are written about a person by someone else, using information gathered from various sources (including primary sources).
Therefore, a diary is the only primary source among the given options.