Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
Q:1/8=120
M:2/4
K:G
['G2 D2 B2 G2 dBGE DzDE/F/ GzG', 'dd d2 dd egfe d3 d dccc']  
X:1
L:1/8
Q:1/8=120
M:2/4
K:G
"^A" G2 D2 | B2 G2 | dBGE | DzDE/F/ | GzG z | GzBc ||"^B" d2 dd | d2 dd | egfe | d3 d | dccc | 
 cBBB | dcBA | GzB z ||  