Answer:
dates.
Step-by-step explanation:
The timeline should always include dates.
It is the display, often in graphic form, of the chronological events, meaning they are presented in the order in which they happened. Besides every event, there should be a clear date or a year when the event has happened.
Timelines are useful for realizing the complete sequence of events, putting historical things into context, and memorizing key years and dates. It provides a clear cut scheme of the way things have developed and happened.