Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:9/8
K:C
['GAG GEG GEG', 'c2 c edc', 'EGc cGE cGE', 'ceg gec dBG']  
X:1
L:1/8
M:9/8
K:C
|: GAG GEG GEG | GAG G2 E ABc | GAG GEG GEG | ABA A2 G ABc :: c2 c edc BAG | c2 c edc e2 g | 
 c2 c edc BAG | ABA A2 G A2 c :: EGc cGE cGE | EGc c2 E ABc | EGc cGE cGE | ABA A2 G ABc :: 
 ceg gec dBG | ceg g2 c f2 d | ceg gec dBG | ABA A2 G A2 c :|  