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:G
['D GF GA']  
X:1
L:1/8
M:2/4
K:G
 D | GF GA | FG z (G/A/) | Bc de | dc z (B/c/) | dd eB | d(c/)B/ AG | EG GF | A2 z | D | GF GA | 
 F3/2 F/ G F/G/ | AB cd | cB z B/c/ | d/d/ de B | d2 cA/F/ | GD GA | G3 ||  