Final answer:
Section A's return in movement 2 of Eine Kleine Nachtmusik differs in instrumentation, providing contrast by altering which instruments are highlighted.
Step-by-step explanation:
When section A returns for the second time in the second movement of Eine Kleine Nachtmusik, it is different primarily in terms of instrumentation.
The texture may be thinned to feature a solo or a reduced number of instruments, or a different set of instruments may be highlighted. This change provides contrast and keeps the return of the theme fresh to the listener.
Changes in tempo, key, and rhythm could also occur in other sections or movements, but in this case, the changes to the instrumentation are noteworthy. As with many classical pieces, variations in repeated sections are common to provide interest and dynamic contrast.