Implement a $4-$bit unsigned selective $2$s complementer. It should take $4$bits D $=$D$3...$D$0$ as output. It should output when A C $=0$ A $=$A$3...$A$0$ and C as input, $,$ the unsigned $2$s complement of when A C $=1.$ Save the circuit as c$6.$cct $.($Hint: use your $4-$bit binary plus $1$ incrementer$)$