Craft a musical composition that adheres to the specified musical theme and letter-based structure.
X:1
L:1/8
M:4/4
K:G
['dc B2 d2 (3efe d2 ga bg', "d'b gb"]  
X:1
L:1/8
M:4/4
K:G
 dc | B2 d2 (3efe d2 | ga bg (3efe dc | Bd gd ef gb | a2 a2 a2 dc | B2 d2 (3efe d2 | 
 ga bg (3efe dc | Bd gd ef gb | a2 a2 g2 :| bc' | d'b gb d'b gb | ga bg (3efe dc | Bd gd ef gb | 
 a2 a2 a2 bc' | d'b gb d'b gb | ga bg (3efe dc | Bd gd ef gb | a2 a2 g2 :|  