Answer: B. to establish a sense of change over time.
Explanation: When historians use chronology, they add all events, not just the major events that changed history. Historians can't trace every recorded year in history either, especially since they weren't alive at the time of the event. There aren't any themes when it comes to tracing back events, because it isn't a story we're looking for, it's the events of history. Showing that history is best understood in eras doesn't make sense because it's too broad of a timeframe to aim for eras.
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