Develop a musical piece using the given theme and incorporating the letter-based structure provided.
X:1
L:1/8
M:2/4
K:C
['G c>d ec f2 eg ec dB', 'z e/f/ gg fe', 'ge ge/f/']  
X:1
L:1/8
M:2/4
K:C
 G | c>d ec | f2 eg | ec dB | c2 z G ||"^A" c>d ec | f2 ed | cB AB | d/c/B/A/ GG | c>d ec | f2 eg | 
 ec dB | c2 z e/f/ |"^B" gg fe | f2 z e/f/ | gg fe | d2 z e/f/ | gg fe | fg ag | fe dc | 
 d/c/B/A/ GG |]"^Sortie" ge ge/f/ | ge ge/f/ | gg ee | d/e/f/d/ ee/f/ | ge ge/f/ | ge ge/f/ | 
 gg ee | d/e/f/d/ !fermata!c2 |]  