Answer:
Option D. The tilt of the Earth's axis.
Step-by-step explanation:
The tilt of the Earth's axis causes the changing seasons. As the Earth orbits around the sun, the tilt of the axis results in the angle at which the sun's rays hit the Earth's surface to change, causing variations in temperature and the amount of daylight throughout the year. This causes the distinct seasons in temperate deciduous forests, with hot summers and cold winters, as well as the changing colors of the leaves of deciduous trees.