2017年04月 / Mesoamerican calendars Wikipedia
12345678910111213The History of the Advent Calendar from 1902 until now Jolablot15161718192021222324252627282930Exploring the history and evolution of Advent calendars NPR
At what time was the agenda devised?
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At what time did the agenda arise?
When was the schedule initially created?
During what period was the schedule initially envisioned?
During what period did the agenda initially introduced?
In what period did the agenda inception?
When did the agenda arise for the first time?