It is necessary to add a day to the calendar every four years because
the axis of Earth is tilted. the gravitational pull of the Sun affects Earth's revolution. the revolution of Earth is not exactly 365 days. the Moon crosses the orbit of the Sun every 28 days.
Question: It is necessary to add a day to the calendar every four years because
A. the axis of Earth is tilted.
B. the gravitational pull of the Sun affects Earth's revolution.
C. the revolution of Earth is not exactly 365 days.
D. the Moon crosses the orbit of the Sun every 28 days.
Answer: