Equatorial regions are characterized by their proximity to the equator, which results in a unique climate. These regions experience a small annual temperature range, as indicated by option 'C'. Let's delve into the factors that contribute to this characteristic.

Factors contributing to a small annual temperature range in equatorial regions:
1. Proximity to the equator: Equatorial regions are located near the equator, where the sun's rays are most direct throughout the year. This leads to a relatively consistent amount of solar radiation received throughout the year, resulting in a stable temperature range.

2. Low seasonal variations: Equatorial regions experience minimal seasonal variations due to their proximity to the equator. The angle at which the sun's rays hit the Earth remains relatively constant, resulting in consistent temperatures throughout the year.

3. Absence of distinct seasons: Equatorial regions typically lack distinct seasons, such as spring, summer, autumn, and winter, that are commonly observed in other parts of the world. Instead, they usually have two main seasons: wet and dry. This lack of seasonal variation further contributes to the small annual temperature range.

4. High humidity: Equatorial regions are known for their high levels of humidity, which helps to moderate temperature fluctuations. The presence of moisture in the air acts as a heat sink, absorbing and releasing heat slowly, thus maintaining relatively stable temperatures.

5. Ocean currents: Equatorial regions often experience the influence of ocean currents, which can help regulate temperatures. For example, the presence of cool ocean currents can mitigate excessive heating, while warm currents can elevate temperatures slightly.

Conclusion:
In summary, equatorial regions are characterized by a small annual temperature range due to their proximity to the equator, low seasonal variations, absence of distinct seasons, high humidity, and the influence of ocean currents. These factors work in combination to create a relatively stable and consistent climate throughout the year.

Equatorial regions have a small annual temperature range, which is mentioned as approximately 3 degrees Celsius in the text.