The correct answer is option 4: Tropical no-wind belt. The doldrums refer to a region near the equator characterized by calm and light winds. In this area, the trade winds from the northern and southern hemispheres converge, causing a region of low pressure where the air is rising. As the air rises, it cools and condenses, leading to frequent cloud cover and precipitation. The lack of strong winds in this region makes it difficult for sailing ships to navigate, leading to the term "doldrums" being used to describe a state of boredom or inactivity. It is important to note that while there may still be some light winds in the doldrums, they are generally not strong or consistent enough to be relied upon for sailing purposes. Therefore, option 4 accurately describes the doldrums as a tropical no-wind belt.