Obbligato is defined as:

• A. A short piece preluding an aria
• B. A Baroque suite
• C. A drone accompaniment
• D. An extended solo, often accompanying the vocal part of an aria

Answer: (D)

Obbligato refers to a written-out instrumental line that is essential to the music of a vocal piece, especially an aria. It is an extended, often virtuosic part performed by a specific instrument that accompanies and interacts with the vocal melody, giving the instrumental line a defined role rather than simply filling background space. Because the obbligato line is integral to the texture and can stand with its own musical argument alongside the voice, this description fits best: an extended solo that accompanies the vocal part of an aria.

This isn’t about a short preludial piece, a Baroque suite, or a drone. A short introduction would be preludial or instrumental intro; a Baroque suite is a collection of dances; a drone is a sustained pitch under the music—none of these capture the idea of a specifically notated, ongoing instrumental line that is “obligatory” to the aria itself.