Generate a piece of music. It is monophony.  
X:1
T:Music21 Fragment
C:Music21
L:1/8
Q:1/4=78
M:2/4
I:linebreak $
K:D
V:1 treble 
V:1
 DE | FA AA | Ad dd | dB BB | B2 d>B | AF FF | GF ED | FE E>F | E2 DE | FA AA | Ad dd | dB BB | %12
 B2 d>B | AF FF | GF ED | EA BA | D2 CD | EE ^DE | FF B>A | ^GG AB | c2 cd | ec A^G | F^G AB | %23
 cd cB | A3 F/^G/ | A/B/A/^G/ Ad | dF F>F | AE EA | F3 F/G/ | A/B/A/^G/ Ad | dF FB | AE EA | %32
 D3 x || %33  