Generate a piece of music. It is monophony.  
X:1
T:Music21 Fragment
C:Music21
L:1/8
Q:1/4=72
M:2/4
I:linebreak $
K:G
V:1 treble 
V:1
 D | GB Ac/c/ | B/B/d GG/A/ | B/B/c de | A3 D | GB Ac/c/ | B/B/d GG/A/ | BB AA/A/ | G3 D | %9
 GB Ac/c/ | Bd G>A | B>c de | A3 D | GB Ac | B/d/d/B/ GG/A/ | B>c AA | G3 z | d>d e>d | B d2 D | %19
 G>G AA | B3 D | GB Ac | B/d/d/B/ GG/A/ | B>c AA | G3 D | GB Ac/c/ | B/B/d GG/A/ | B/B/c de | %28
 A3 D | GB Ac/c/ | B/B/d GG/A/ | BB AA/A/ | G3 D | GB Ac/c/ | Bd G>A | B>c de | A3 D | GB Ac | %38
 B/d/d/B/ GG/A/ | B>c AA | G3 z | d>d e>d | B d2 D | G>G AA | B3 D | GB Ac | B/d/d/B/ GG/A/ | %47
 B>c AA | G3 z || %49  