Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/16
M:2/4
K:A
['ec ec', 'cd edcd e2 fe dcBc d2 ed']  
X:1
L:1/16
M:2/4
K:A
 cd | ec ec eagf | ec ec eagf | ec ec fedc | d2B2B2 cd | ec ec eagf | ec ec eagf | efde cAcG | 
 E2A2A2 :: cd | edcd e2 fe | dcBc d2 ed | cAcA dcBA | B2B2B2 cd | edcd e2 fe | dcBc d2 ed | 
 caAe dfBd | E2A2A2 :|  