Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:4/4
K:Bb
['z C']  
X:1
L:1/8
M:4/4
K:Bb
 z G | G2 c2 c2 (Bc) | d3 (c/)B/ A2 F2 | G6 A2 | B G3 F(G/)F/ EF/G/ | G4 z2 z C | C2 G2 F2 ED | 
 E2 C2 G,/ G,3/2 z C | E2 E2 F3 D/B,/ | C4 z2 ||  