Duo (pinyin: duó) is a bronze percussion instrument of the Chinese Bronze Age, similar to a bell but slightly larger. Shaped like a nao, zheng and with a tongue, it was used in ancient times to announce political and religious laws. Prevalent in China from the Spring and Autumn to the Han Dynasty. Mostly used in the military. Its shape is slightly similar to the Yongzhong, but smaller than the bell. The handle is short and square. Body cavity with or without tongue. Those with tongues can shake and make sounds. The overall shape is similar to that of bronze musical instruments such as bells, mussels, cymbals, sentences, and zheng, but the difference is that there is a tongue in the cavity. Tongues are made of copper and wood. The wooden tongue is called Muduo, and the copper tongue is called Jinduo. The top of the cavity has two forms: one has a stubby, hollow square bronze handle, which can be inserted with a wooden handle; the other has a long bronze handle. When in use, shake it with the handle, and the tongue hits the cavity to make a sound.
According to the "Analects of Confucius", an official sighed after seeing Confucius: "The world has been without Tao for a long time, and the heaven will take the Master as Mu Duo." As a result, Mu Duo became a symbol of teachers and education in later generations. Normal colleges and universities such as Beijing Normal University, Northwest Normal University, National Taiwan Normal University, Qufu Normal University, Gannan Normal University, and National Changhua Normal University all use the symbol of Muduo on their school badges. The Ministry of Education of the Republic of China named the award given to outstanding teachers as the "Teacher Award".