Milankovitch cycles refer to . A. changes in Earth-Sun relationships, namely the Earth's orbit around the sun, the Earth's axial rotation, and the Earth's axial tilt. B. cyclical changes in solar irradiance caused by increases and decreases in sunspot activity. C. increases and decreases in atmospheric gases and aerosols, primarily caused by natural activity such as volcanic activity and changes in net primary productivity. D. tectonic changes in continental position.