Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/4
M:3/4
K:D
['f f', 'f f']  
X:1
L:1/4
M:3/4
K:D
 f f f | f a/f/g/e/ | f F F | F A/F/G/E/ | F d B | e/f/ c2 | B A d |{f} c3 :: c c c | c e/c/d/B/ | 
 c f f | f A/F/G/E/ | F g f |{f} e2 d | c/e/d/A/F/E/ | F3 :|  