Adam and his family are planning a trip to Alaska in either June or December. During the summer months in the Northern Hemisphere, the weather is typically warmer and the days are longer. During the winter months in the Northern Hemisphere, the weather is typically cooler and the days are shorter. Adam’s family decides to travel in June based on this information. Why does Earth have seasons?

A. because Earth rotates on its axis as it revolves around the sun
B. because Earth's axis is tilted as it revolves around the sun
C. because the moon blocks the sun during the winter months
D. because the moon's gravitational pull is stronger during the summer months