Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/16
Q:1/4=104
M:2/4
K:D
['', 'a2>b2 a2f2d2 f2 gfef gfef gfed c2A2', 'e2A2 (ba^ga) f2 A2 :|2 gfef gbac']  
X:1
L:1/16
Q:1/4=104
M:2/4
K:D
 A2 |:"D" d2f2 a2>b2 | a2f2d2 f2 |1"A7" gfef gfef | gfed c2A2 :|2"A7" gfed cABc |"D" d2d2d2 :| 
[K:A] e2 |:"A" e2c'a e2ac | c2ec A2c2 |1"E7" d2d2 dcB2 |"A" c2c2 cBA2 :|2"E7" dcBc defg | 
"A" a2a2a2 :|[K:D] A2 |:"D" f2A2 d2A2 | FAdf a2>f2 |1"A7" g2A2 e2A2 | (ba^ga) f2 A2 :|2 
"A7" gfef gbac |"D" d2d2d2 :|  