Which of the following was a direct predecessor of the piano?

The xylophone is a percussion instrument made of wooden bars struck with mallets. It does not share the keyboard mechanism or the same musical lineage as the piano and therefore cannot be considered a predecessor.

The violin is a string instrument that is played with a bow and does not utilize a keyboard. Although it shares the broader category of string instruments with the piano, it does not have a direct historical connection or influence in the development of keyboard instruments.

The harp is a stringed instrument played by plucking the strings. While it has a longstanding history in music, it does not utilize a keyboard mechanism and is not considered a direct predecessor to the piano, which evolved from keyboard-based instruments.

The zither is an acoustic string instrument that is typically played by plucking or strumming. Like the harp, it lacks a keyboard and does not contribute to the evolution of keyboard instruments such as the piano.