What is a characteristic of a perfect authentic cadence?

A perfect authentic cadence is characterized by the dominant chord (V) moving to the tonic chord (I), with specific requirements for both root movement and voice leading. In this case, the correct answer emphasizes the importance of the bass notes and the position of the highest note in the final chord, which is indeed the tonic.

Both chords must have their roots sounding in the bass—this means that the V chord should have its root note in the bass (usually the fifth degree of the scale) and the I chord should have its root (the tonic) also sounding in the bass. Moreover, for it to be deemed "perfect," the highest note in the final tonic chord must be the tonic note itself. This combination establishes a strong resolution and clarity to the tonality.

The other options do not define a perfect authentic cadence correctly. The mention of an augmented sixth chord relates to different harmonic progressions and does not conform to the standard V to I resolution. Similarly, while perfect authentic cadences can indeed occur in minor keys, this trait alone does not define them, as they are fundamentally linked to the quality and placement of the chords. Lastly, the leading tone chord may feature in various cadences but does not specifically define a perfect authentic cadence.