Answer:
A source in history is any source or resource that offers knowledge about a historical event. This source is classed as a primary source if it was written during the historical event under consideration and so provides a first-hand account of the event, or as a secondary source if it combines primary sources to produce a new source. Sources are also thought to be beneficial or effective if they provide knowledge on a historical event. As a result, a letter written during the time of a historical event would be called a "useful primary source document" because it is a first-hand account of the historical event being studied (primary source) as well as providing information about it, making it a useful document.
Step-by-step explanation:
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