Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:2/4
K:D
['FA GB Ad fd cd', 'dc B/c/d/B/ AF']  
X:1
L:1/8
M:2/4
K:D
|: FA GB | Ad fd | cd eA | FA dA | FA GB | Ad fd | cd ec | ed d2 :: dc B/c/d/B/ | AF FE/F/ | 
 GF EF/G/ | FD DA | dc B/c/d/B/ | AF F^G/A/ | Be ec | ed d2 :|  