Aseason is a subdivision of the year, marked by changes in weather, ecology, and hours of daylight. seasons result from the yearly revolution of the earth around the sun and the tilt of the earth's axis relative to the plane of revolution. in temperate and polar regions, the seasons are marked by changes in the intensity of sunlight that reaches the earth's surface. these variations may cause animals to go into hibernation or to migrate, and plants to be dormant. it is scientifically fascinating how bears and other animals instinctively know when to hibernate. during may, june and july, the northern hemisphere is exposed to more direct sunlight because the hemisphere faces the sun. the same is true of the southern hemisphere in november, december and january. it is the tilt of the earth that causes the sun to be higher in the sky during the summer months which increases the solar flux.

which sentence is unnecessary and could be eliminated without disturbing the flow and information of the paragraph?

a. these variations may cause animals to go into hibernation or to migrate, and plants to be dormant.
b. it is scientifically fascinating how bears and other animals instinctively know when to hibernate.
c. it is the tilt of the earth that causes the sun to be higher in the sky during the summer months which increases the solar flux.
d. seasons result from the yearly revolution of the earth around the sun and the tilt of the earth's axis relative to the plane of revolution.