Answer:
1. Elliptical orbit.
2. Tropic of Cancer.
3. Winter season.
Step-by-step explanation:
The movement of the earth is the primary cause for the yearly variation. The earth rotates at its axis and moves around the sun in an orbit which is not a perfect circle but is elliptical.
During the June Solstice, that occure on 21st June every year, the vertical rays of the sun strike the Tropic of Cancer.
The condition of the Earth is tilted at 23.4 degrees which becomes the primary reason for the short days in the winter season and long days in the summer seasons.