从易到难:
prelude 6
Prelude 8,22
Prelude 1,4, 10,14,12,17
Prelude 2
Prelude 9,18,19,21
Prelude 5,11,13,·15,16,20
Prelude 3
Prelude 7,23
Prelude 24
prelude 6
Prelude 8,22
Prelude 1,4, 10,14,12,17
Prelude 2
Prelude 9,18,19,21
Prelude 5,11,13,·15,16,20
Prelude 3
Prelude 7,23
Prelude 24