Simplify the following Boolean functions in SOP form, using Karnaugh maps:

$($a$)F(x,y,z)={\displaystyle \underset{?}{\overset{?}{}}}(2,3,6,7)$

$($b$)F(A,B,C,D)={\displaystyle \underset{?}{\overset{?}{}}}(4,6,7,15)$

$($c$)F(A,B,C,D)={\displaystyle \underset{?}{\overset{?}{}}}(3,7,11,13,14,15)$