Why Do We Have Seasons on Earth

Why do we have seasons on Earth?

A) As Earth goes around the Sun and Earth's axis remains pointed toward Polaris,the Northern and Southern hemispheres alternately receive more and less direct sunlight.
B) The tilt of Earth's axis constantly changes between 0 and 23 1/2°,giving us summer when Earth is tilted more and winter when it is straight up.
C) Earth's distance from the Sun varies,so that it is summer when we are closer to the Sun and winter when we are farther from the Sun.
D) Seasons are caused by the influence of the planet Jupiter on our orbit.