Final answer:
Earth's axis of rotation is tilted about 23.5° relative to the plane of its orbit around the Sun, which is also known as the ecliptic plane. This axial tilt is responsible for the changing seasons and affects the Earth's precession.
Step-by-step explanation:
The Earth's axis of rotation is tilted at an angle of about 23.5° relative to the plane of its orbit around the Sun. This inclination of Earth's axis relative to the plane of the ecliptic has several important consequences for our planet. It causes the seasonal changes we experience as the angle of sunlight changes throughout the year. It also affects the Earth's precession, which is the slow, conical movement of the axis of rotation that cycles approximately every 26,000 years, during which the axis points to different parts of the sky.
Therefore, the correct answer to the student's question is E. The axis of its orbit around the Sun. Earth's axis is always tilted at about 23.5° relative to a line perpendicular to the ecliptic plane, which is the imaginary plane that encompasses Earth's orbit around the Sun.