The correct answer is option 4, Equator. The Equator experiences the least annual range of temperature compared to the other options provided.

Option 1, the Arctic Circle, experiences extreme temperature fluctuations throughout the year. It has a wide range of temperature, with very cold winters and relatively mild summers.

Option 2, the Tropic of Capricorn, also experiences a significant annual range of temperature. It has hot summers and cool winters, which leads to a larger difference in temperature throughout the year.

Option 3, the Tropic of Cancer, has a similar climate to the Tropic of Capricorn. It also experiences a relatively large annual temperature range.

On the other hand, option 4, the Equator, experiences a consistent climate throughout the year. It is located near the center of the Earth and receives direct sunlight year-round. This results in a small annual range of temperature, with relatively constant temperatures that hover around the same point throughout the year.

Therefore, the Equator experiences the least annual range of temperature compared to the other options.