In what situation must an aircraft be placed to initiate a spin?

To initiate a spin, an aircraft must be in a condition where both wings are stalled, which means that the critical angle of attack has been exceeded on both wings. This condition leads to an uncontrolled descent and a distinct rotational motion about the vertical axis. When both wings are stalled, airflow over the wings is disrupted, resulting in a loss of lift and asymmetrical aerodynamic forces, which is crucial for the onset of a spin.

In the context of the other choices, having one wing in a high-speed state does not contribute to spin initiation, as spins typically arise from an imbalance of lift and stall characteristics across the wings. Additionally, being in level flight alone does not result in a spin; the aircraft must be subject to a specific set of conditions, primarily the stall condition, which differs from maintaining level flight. Finally, while stalling one wing can contribute to the dynamics of a spin, simply stalling the left wing alone is not sufficient to initiate a spin; both wings must be stalled to create the necessary rotational force.