A is a Lattice. (Lattice A is one of the tricky examples used many times for asking whether it is Distributive lattice or not... And It is NOT a Distributive lattice (It contains the Standard Pentagon Lattice as Sublattice which makes it Not Distributibve) )
B is Not a lattice. Because $\left \{ 3,5 \right \}$ doesn't have LUB or $\left \{ 2,6 \right \}$ doesn't have GLB.
$UB\left \{ 3,5 \right \} = \left \{ 2,6,1 \right \}//\,\,NO \,\,LUB$
$LB\left \{ 2,6 \right \} = \left \{ 3,5,4 \right \}//\,\,NO \,\,GLB$
C is Not a Lattice. One reason being There is No Greatest Element and Every Finite lattice must have Greatest and least elements. Other Reason, $\left \{ 2,4 \right \}$ doesn't have LUB or $LB\left \{ 5,1 \right \}$ doesn't have LUB and GLB.
$UB\left \{ 2,4 \right \} = \left \{ 5,1 \right \}//\,\,NO \,\,LUB$
$LB\left \{ 5,1 \right \} = \left \{ 3,6,2,4 \right \}//\,\,NO \,\,GLB$
D is a lattice. Every pair of elements have both GLB and LUB.
