Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:2/4
K:D
['A2 (G/F/E/D/) B2 A2 Bgec', 'fgab e2 A2']  
X:1
L:1/8
M:2/4
K:D
|: A2 (G/F/E/D/) | B2 A2 | Bgec | dAFD | A2 (G/F/E/D/) | B2 A2 | Bgec | (cd) d2 :: fgab | e2 A2 | 
 fgab | e2 A2 | a2 (fd) | gbag | ff (e/g/)(e/c/) | (cd) d2 :|  