Level 5. According to the inquiry of the Central Conservatory of Music, Bach's unaccompanied flute suite in BWV 10 13a minor is the same as "Cello No.1 without accompaniment" in spectral difficulty, and the Central Conservatory of Music has designated it as the fifth level of the textbook. The cello suite is Bach's famous work. If Bach is regarded as a master among the masters by musicians of all ages, then his six cello suites for cello solo are classics.