Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:D
['dB A2 dB GBdB GA A/A/A', 'ad d/d/d']  
X:1
L:1/8
M:4/4
K:D
 e | dB B/B/B dA A/A/A | B2 dB A2 dB | GBdB GA A/A/A | fe e/e/e edBd | fd d/d/d eB B/B/B | 
 d2 dB A2 dB | GBdB GA A/A/A | edBc ddd :| f | (3aaa ag ad d/d/d | Bd d/d/d ad d/d/d | 
 Be e/e/e edef | gefd efge | (3aaa ag ad d/d/d | Bd d/d/d ad d/d/d | (3efg af gecd | edce dddf | 
 (3aaa ag ad d/d/d | Bd d/d/d ad d/d/d | Be e/e/e edef | gefd efge | fd d/d/d eB B/B/B | 
 dA A/A/A BGGA | (3aaa af edBe | dBAB d3 ||  