Answer:
A documentary made ten years later.
Explanation:
A secondary source is one which interprets or analyzes primary sources. This means that secondary sources are those that are one or more steps removed from a particular event. A documentary would be an example of this because it was not made at the same time as the event that is being studied (in this case, it was ten years later) and because it is likely to have used primary sources as a source of information. Sometimes, deciding whether a source is primary or secondary can be difficult.
