a$.$ What is the correct sum$-$of$-$products expression for this gate's behaviour?

$T\frac{?}{b}=ar(A)\frac{*}{b}ar(B)$

$T\frac{?}{b}=ar(A)\frac{+}{b}ar(B)$

$T\frac{?}{b}=ar(A*B)$

$T=A+B$

b$.$ This device corresponds to one of the derived gates that were introduced in lecture $6.$ Which type is it$?$

NAND gate: $T\frac{?}{b}=ar(A*B)$

NOR gate: $T\frac{?}{b}=ar(A+B)$

XOR gate: $T=Ao+B$

XNOR gate: $T\frac{?}{b}=ar(Ao+B)$