Option 1: Formulation and initial stage

This option is correct. The mentioned characteristics of a warm sea temperature (> 26°C), high relative humidity (> 700m), and atmospheric instability are all associated with the formulation and initial stage of a tropical cyclone. During this stage, the warm sea temperature provides the energy source for the cyclone to develop. The high relative humidity at a height of > 700m indicates the presence of moist air which is necessary for the formation of clouds and precipitation. Atmospheric instability refers to the condition where warm, moist air rises rapidly, creating an unstable atmosphere that can fuel the development of the cyclone. Therefore, all these characteristics are essential for the formulation and initial stage of a tropical cyclone.

Option 2: Modification stage

This option is incorrect. The mentioned characteristics are not specific to the modification stage of a tropical cyclone. The modification stage typically involves changes in the structure and intensity of the cyclone, which may be influenced by factors such as wind shear and interactions with other weather systems.

Option 3: Full maturity

This option is incorrect. The mentioned characteristics are not specific to the full maturity stage of a tropical cyclone. In the full maturity stage, the cyclone reaches its peak intensity and often produces strong