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Which of the following factors contribute to the periodic changes in Earth's temperature known as the Milankovitch cycles? Select the THREE correct answers.

A): Earth wobbles slightly on its axis

B): The concentration of carbon dioxide in Earth's atmosphere is decreasing

C): Earth's atmosphere has been enriched in oxygen by cyanobacteria

D): Earth's orbit alternates between a circular and an elliptical shape

E): Earth's axial tilt varies between 22 and 24 degrees

F): Earth's shape is spherical