What conditions must be met for spin training?

The correct answer highlights that for spin training, it is essential to conduct the exercises under visual meteorological conditions (VMC) during the daytime and with a discernable horizon. This ensures that a pilot can maintain visual reference to the ground or surrounding environment, which is crucial for executing spin maneuvers safely and effectively.

Having a discernible horizon allows the pilot to make necessary corrections and recover from spins with better awareness of their aircraft's orientation and position. This is particularly important because spin recovery relies on the ability to visualize and respond to the aircraft's attitude and altitude effectively.

In contrast, options involving conditions such as night VMC or a cloud deck below can severely limit visibility and situational awareness, making it difficult for the pilot to execute spins safely. Engaging in spin training without a clear visual reference would significantly increase the risk of losing control of the aircraft, which is why those conditions do not meet the requirements for conducting such training.