Task: Question Generation
Input (English): Samuel Adelstein described the Lombardi mandolin in 1893 as wider and shorter than the Neapolitan mandolin, with a shallower back and a shorter and wider neck, with six single strings to the regular mandolin's set of 4. The Lombardi was tuned C, D, A, E, B, G. The strings were fastened to the bridge like a guitar's. There were 20 frets, covering three octaves, with an additional 5 notes. When Adelstein wrote, there were no nylon strings, and the gut and single strings "do not vibrate so clearly and sweetly as the double steel string of the Neapolitan."
Output (English): How many frets did the Lombardi have?