Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:2/4
K:D
['DF AF GB']  
X:1
L:1/8
M:2/4
K:D
 A | DF AF | GB A/ G3/2 | FA GF | ED CA, | DF AF | GB d/d/ d/B/ | AA AF | GD | D2- | D3 A | 
 Bc d3/2 B/ | d3/2 B/ AF | EG FE | DE A3/2 A/ | Bc dB | dB AF | EG F3/2 E/ | FE D ||  