Primary sources may be objects (artifacts, tools, weapons, inventions, fashions, uniforms), images (photographs, film, video), audio (oral histories, music, interviews, speeches,) or documents (books, letters, journals, diaries).
A primary source gives you direct access to the subject of your research. Secondary sources provide second-hand information and commentary from other researchers. Examples include journal articles, reviews, and academic books. A secondary source describes, interprets, or synthesizes primary sources.
If a country export a greater value than imports, it has a trade surplus or positive trade balance, and conversely, if a country imports a greater value than export, it has a trade deficit or negative trade balance
