They offer information indirectly and are a stage far from the event under review.
These are issues such as documentaries biographies, encyclopedias.
Such things can be included by them as video recordings or interviews, memoirs, periodicals, speeches, schedules, manuscripts, pictures.
They could even be formerly published investigation stories, such as results or clinical studies of trials. Bring and secondary sources are another hand bill of gatherings and are used to interpret ideas concerning the events noted in major sources.
Considering major and supplementary resources is an essential step that requires before starting to write your research reports, to be taken.