Many questions at exam level will require candidates to demonstrate their knowledge on how to handle evidence. An examiner will expect the better answers to contain certain terminology which shows that a candidate does not necessarily take evidence for granted. Such terminology would include primary evidence, secondary evidence, reliable and bias. All candidates need to know what each of these words mean.
Primary evidence is evidence that actually comes from the time being studied in the question.
The memories of survivors would be primary evidence. Film of the ship leaving harbor would be primary evidence. Secondary evidence is the opposite of primary. This is evidence that does not come from the time being studied. Historians frequently produce secondary evidence.