Final answer:
Theme A returns at the end of the second movement of Beethoven's Fifth Symphony in the same key, providing unity and completeness to the symphony.
Step-by-step explanation:
At the end of the second movement of Beethoven's Fifth Symphony, theme A returns in the same key as the beginning of the movement, which is C minor. This return emphasizes the cyclical nature of the symphony and provides a sense of unity and completion. Additionally, Beethoven adds new variations and developments to theme A, showcasing his creativity and mastery of musical form.