Compose a piece using the specified musical pattern based on the alphabet and the provided melodic theme.
X:1
L:1/8
M:3/4
K:F
['B_AG F2']  
X:1
L:1/8
M:3/4
K:F
 CCC | F3 _AGF | E2 z G_AB | c3 B_AG | F2 z CCC | F3 _AGF | E2 z G_AB | c3 B_AG | F2 z ccc | 
 c3 G_AF | G2 z CF_A | G3 B_AG | F2 z |]  