The horse latitudes are regions located at approximately 30 degrees north and south of the equator. These regions lie within the atmospheric pressure belts known as the subtropical highs. The correct option is option 3 - subtropical high.

The subtropical highs are characterized by high atmospheric pressure and sinking air. As air near the equator rises due to heating, it moves poleward and cools. As it cools, it becomes denser and sinks back down to the surface in the subtropical high pressure belt.

In this sinking motion, the air becomes drier and suppresses the formation of clouds and precipitation. As a result, the horse latitudes are often associated with arid and semi-arid regions in both the Northern and Southern hemispheres.

Option 1, polar high, refers to the regions near the poles where cold air sinks and creates high atmospheric pressure. Option 2, equatorial low, refers to the area near the equator where the rising air creates a low-pressure zone. Option 4, sub-polar low, refers to the regions between the polar high and the horse latitudes where low-pressure systems are common.

Alert - correct answer should be option 3.