Compose a piece of music that follows both the given musical theme and the letter-based structure provided.
X:1
L:1/8
M:3/4
K:Bb
['cd c2 F2 B3 c d2']  
X:1
L:1/8
M:3/4
K:Bb
 F2 | B2 D2 FF | B4 dB | c3 dec | d4 z2 | cd c2 F2 | B3 c d2 | cd c2 F2 | B3 c d2 | ec d2 c2 | 
 B4 z2 |]  