Select the odd one out. Guitar, Veena, Piano, Violin

The violin is the smallest and highest-pitched of the instruments in the string family where sound is produced by drawing the bow across one of the four strings or by plucking the string with a finger. The piano is a large keyboard musical instrument with a wooden case enclosing a soundboard and metal strings, which are struck by hammers when the keys are depressed. The Guitar is a stringed musical instrument where the strings are plucked with the fingers or with a plectrum to generate sound. The Veena is a string based Indian classical music instrument. The violin, guitar and veena belong to the string family whereas Piano is played using keys.