Which instrument typically consists of a single string on a curved stick?

The musical bow is a simple yet ancient instrument that typically consists of a single string stretched across a curved stick, which allows it to produce sound when plucked or struck. This design creates a unique acoustic quality, with the curvature of the bow contributing to the resonance and tonal character. The simplicity and portability of the musical bow have made it an integral part of many cultures' musical traditions, often used in folk music and rituals.

In contrast, the banjo, lyre, and guitar each have multiple strings and more complex constructions. The banjo has a circular body with a drum-like head and typically features several strings for more intricate playing. The lyre is an ancient stringed instrument that usually has multiple strings held in an arched frame, often bringing a more harmonic texture. The guitar, being one of the most popular string instruments, has six strings stretched over a flat body, allowing for a broader range of musical expression. Thus, the simplicity and unique structure of the musical bow distinguish it as the correct answer.