<human>:  What are the differences between a violin, viola, and a cello?
<bot>: The differences between a violin, a viola, and a cello are in their size, shape and range of sound. The violin is the smallest and highest pitched of the three instruments, with a range of about three octaves. The viola is slightly larger than the violin and lower in pitch, with a range of about four octaves. The cello is the largest and lowest pitched instrument, and has a range of about four and a half octaves. The construction of the instruments also varies among each string instrument, as the thickness of the strings affects the instruments’ respective sounds.