Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/16
M:2/4
K:G
['G2DD D2B2 cBAc B2>A2 GFGA', 'GBdB GBdB cBAc']  
X:1
L:1/16
M:2/4
K:G
 (3DEF | G2DD D2B2 | cBAc B2>A2 | GFGA G2B2 | AGAB A2(3DEF | G2DD D2B2 | cBAc B2>A2 | GFGA BAGF | 
 G2GG G2 :: D2 | GBdB GBdB | cBAc B2>A2 | G2GG G2B2 | AGAB c2A2 | GBdB GBdB | cBAc B2>D2 | 
 D2G2 B2d2 | dcBA G2 :|  