Which type of document is least likely to be a primary source?

The correct answer identifies a textbook summarizing historical events as the type of document least likely to be a primary source. Primary sources are original materials created during the time under study or by individuals directly involved in the events. They provide firsthand evidence or direct insight into historical moments.

A manuscript from the time being studied, a letter written during the historical period, and a speech delivered at an event all qualify as primary sources because they are original documents that offer direct evidence about the context in which they were created.

In contrast, a textbook is a secondary source as it interprets, analyzes, and summarizes information sourced from primary materials. Textbooks are often written after the fact and provide a compiled view of historical events rather than the firsthand perspective that primary sources offer. Thus, the nature of the textbook as a summarization makes it the least likely to represent primary source material.