What Is the Primary Cause of Earth's Seasons

What is the primary cause of Earth's seasons?

A) The orbit of Earth is an ellipse, so Earth is not always the same distance from the Sun.
B) Earth's rotation axis tilts with respect to the plane of its orbit around the Sun.
C) Earth's precession axis precesses (wobbles) .
D) In accord with Kepler's second law, Earth moves faster during parts of its orbit around the Sun and more slowly during other parts.