Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:Ador
['A3 G B3 A GBdB']  
X:1
L:1/8
M:4/4
K:Ador
 A3 G B3 A | GBdB AGEG | A3 G B3 A | GBdB A4 :|  