Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:2/4
K:Bb
['CD/D/ C2 B,B, G, z B,C/C/ B,2', 'F,2- F,2', 'z B,C/C/ B,2 F,F, D, z F,G,/G,/', 'C,2 B,,B,, F,, z', 'B,,2 B,,G,, F,,2-']  
X:1
L:1/8
M:2/4
K:Bb
 CD/D/ C2 | B,B, G, z | B,C/C/ B,2 ||[M:3/4] G,G, G,2 A,G, ||[M:2/4] F,F, F,2- | F,2 F, z | 
 B,C/C/ B,2 | F,F, D, z | F,G,/G,/ G,2 ||[M:3/4] F,F, F,2 G,F, | D,D, B,,2 z2 || 
[M:2/4] C,C,/C,/ C,2 | B,,B,, F,, z | B,,C,/C,/ B,,2 | B,,G,, F,,2- | F,,4 |]  