recap questions.

ANS of no.1:
Primary sources provide first-hand information.
Secondary sources provide second-hand information.
ANS of no.2:
Historians always use fact to evidence that has been proven to be true and reliable.And check with credibility, consistency and corroboration.
ANS of no.3:
Historians revise their interpretations of past events.Their sources may be different with another historians'.So they compare with the others and get a correct explanations.