Why is it warmer in the summer than it is during the winter?

a.  Earth's axis becomes more tilted.

b.  Days are longer and the Sun's rays are more direct.

c.  The Sun gives off more energy.

d.  The Earth is closer to the sun.

b.  Days are longer and the Sun's rays are more direct.

Here in the Northern Hemisphere, we are actually closer to the sun during winter.  However, we are tilted away from the sun during winter.  This leaves us with longer days and less direct sunlight/energy from the sun.