Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:6/8
K:G
['BGG ABc dgg fdc B2 G ABc', "dga bgf gab c'af g2 a bag"]  
X:1
L:1/8
M:6/8
K:G
 BGG ABc | dgg fdc | B2 G ABc | ADD ABc | BGG ABc | dgg fdc | B2 G ABc |1 AGF G2 A :|2 AGF Gga |: 
 bgf gag | fd^c dga | bgf gab | c'af g2 a | bag afd | g3 fdc | B2 G ABc |1 AGF Gga :|2 AGF G2 A ||  