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 Fd AdFd', 'faab afdf']  
X:1
L:1/8
M:4/4
K:D
 d2 Fd AdFd | GdFd edef | d2 Fd AdFd | gfea fd d2 :| faab afdf | gbaf edeg | faab afdf | 
 gfea fd d2 | faab afdf | gbaf edef | gefd edBA | Bcde fd d2 ||  