Final answer:
The first movement of a Classical concerto typically starts with the orchestra, which presents the main themes before the soloist enters.
Step-by-step explanation:
The typical first movement of a Classical concerto begins with B. the orchestra. A concerto often features a compelling interplay between a soloist and the orchestra, and it traditionally starts with an orchestral exposition. This is where the orchestra presents the main themes of the movement. Only after this does the soloist enter with their own interpretation and elaboration of those themes. A cadenza, which is a virtuosic solo passage, typically occurs near the end of the movement, not at the beginning.