Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
Q:1/4=144
M:4/4
K:G
['', 'AdGd GABc dB A2 ABcA EADA |1', 'dBAB G2']  
X:1
L:1/8
Q:1/4=144
M:4/4
K:G
 d2 |:"^A part" gdBd AdGd | GABc dB A2 | ABcA EADA |1 DFAc BAGd :|2 DFAc BAGB |: 
"^B part" cAEA DFAc | BGDG G,DGB | AFDF A,FCB/c/ |1 dcBA G2 GB :|2 dcBA G2 GA |: 
"^C part" cdfd cAFA | G,B,DB AGED | A,CEA cega |1 dBAB G2 GA :|2 dBAB G2 Gf |:"^D part" gecA FADA | 
 G,B,DG, B,DG,B, | CEAc BAGE |1 DEB,A, G,2 G,f :|2 DE C/B,/A, G,4 |]  