Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:G
['GB- Bd/c/']  
X:1
L:1/8
M:4/4
K:G
|:"G" GB- Bd/c/ BdBA |"G" GB- Bd/c/ Bdgd | GB- Bd/c/ BdBG |"Am" ecBA"G" G2 G,2 ::"G" Bddg dgdB | 
"G" Bddg"D" fa"Am"Ac |"G" Bddg dgdB |"Am" ecBA"G" G2 G,2 :|  