Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:3/4
K:C
['G2 f2 dB']  
X:1
L:1/8
M:3/4
K:C
 GBdf a2 | f2 eceg | GBdf a2 | fe e2 c2 | G2 f2 dB | ceeceg | G2 f2 dB | cg e2 c2 |]  