Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
Q:3/8=88
M:6/8
K:C
['GGG GBc d6 cdd cdd c2 B-', 'z cdd cdc (B>AG-) G3 GGG GBc']  
X:1
L:1/8
Q:3/8=88
M:6/8
K:C
|: GGG GBc | d6 | cdd cdd | c2 B- B2 z :| cdd cdc | (B>AG-) G3 | GGG GBc | (d3/2c/4B/4c-) c3 | 
 BBA GAA | G2 G- G2 z ||  