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.
The answer is because they want to convey what happened in history correctly and if they didn't convey it in chronological order then we wouldn't know it the same way. Basically it's to make sure people would know like why it happened and the reasoning to everything. It could be B or C (I hope), but i'm glad I could help some.
