Every fourth year, our calendar has a(n)

February 29 is a date that usually occurs every four years, and is called a leap day.
This day is added to the calendar in leap years
as a corrective measure, because the earth doesn't orbit the sun in precisely 365 days.
(The Gregorian calendar is a modification of the Julian calendar first used by the Romans.)

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A. is considered an abiotic factor

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