Which of the following instruments is traditionally made with snakeskin and horsehair?

The erhu is traditionally made with snakeskin and horsehair, making it unique among the choices presented. The erhu is a two-stringed bowed instrument from China, and its distinctive sound is produced by the strings being played with a bow that has horsehair. The body of the instrument is typically made from wood, while the sounding board is covered with snakeskin, which contributes to its tonal qualities and resonance.

The combination of these materials has historical and cultural significance in the crafting of the erhu, allowing it to achieve the rich, expressive sound that characterizes its use in both solo performances and orchestral settings. Other instruments listed, such as the pipa and yangqin, have different construction materials, and the didgeridoo is traditionally made from eucalyptus wood. This makes the erhu the only instrument in this group that utilizes both snakeskin and horsehair, firmly establishing it as the correct answer.