Final answer:
The Codetta confirms the key of D major by emphasizing the dominant chord progression, specifically the A major chord in this context, to reinforce D major as the key.
Step-by-step explanation:
The Codetta confirms the dominant key, which in this case is D major, by emphasizing the dominant chord progression. The confirmation of a key within Classical music often involves using a series of chords that stabilize the key. In functional harmony, this is typically achieved through the cadential progression which strongly leads to the tonic, and in the process, firmly establishes the key.
The dominant chord in the key of D major is an A major chord, and the codetta will emphasize this chord or its progression to reinforce D major as the key. This does not necessitate introducing a new motif, modulating to a minor key, or restating the main theme, as those are different musical techniques that serve other purposes in composition.