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
['D2 A,D B,DA,B, DFAF GFEF', 'fdAG FAdf eA A2']  
X:1
L:1/8
M:4/4
K:D
 DC | D2 A,D B,DA,B, | DFAF GFEF | DF F2 Agfe | dBBA BAFE | D2 A,D B,DA,B, | DFAF GFEF | 
 DFBF AF F2 | EDCE D2 :| (3gfe | fdAG FAdf | eA A2 eAeg | fedB BAFA | BdAF FEEg | fdAG FAdf | 
 eA A2 e3 f | gfec dedB | ABde fd :|  