Final answer:
The bridge in the first movement of Mozart's Eine kleine Nachtmusik moves to the key of D minor, providing a tonal contrast typical of classical compositions.
Step-by-step explanation:
The bridge of the first movement of Wolfgang Amadeus Mozart's Eine kleine Nachtmusik moves to the key of D minor. This serenade, which is one of Mozart's most popular works, is initially composed in G major, but like many classical pieces, it explores a variety of key changes throughout its movements.
The move to D minor in the bridge introduces a contrast and adds a depth to the tonality of the movement, which is typical of the classical period's approach to harmony and development within a piece.