Develop a tune that adheres to the given musical structure.
'Sectional: Through Composed'  
X:1
L:1/8
M:2/4
K:G
"^1." B/c/ | dB cA | BGG d/g/ | fAc c/e/ | dGB B/c/ | dB cA | BGG d/g/ | fA c>f | ggg :: 
[K:C]"^2." z | ge/c/ Gc | Ac G2 | f/f/f/f/ dG | e/e/e/e/ cG | ge/c/ Gc | Ac G2 | f/f/f/f/ dG | 
 ccc ::[K:G]"^3" z | db af | ge d B/d/ | c c/B/ A c/e/ | d d/c/ B B/c/ | db af | ge d B/d/ | 
 e e/g/ f f/a/ | gb g ::[K:D]"^4" FG | Af ge | f d/>c/ d B/>A/ | A B/>F/ G A/>G/ | G F/>E/ F F/G/ | 
 Af ge | f d/>c/ d B/>A/ | A B/>F/ G e/c/ | d d/>d/ d :|  