$C1 = G0 + C0.P0$
$C2 = G1 + G0.P1 + C0.P0.P1$
$C3 = G2 + G1.P2 + G0.P1.P2 + C0.P0.P1.P2$
$C4 = G3 + G2.P3 + G1.P2.P3 + G0.P1.P2.P3 + C0.P0.P1.P2.P3$ // read $C4$ as:
Carry is generated in $3^{rd}$ stage OR
Carry is generated in $2^{nd}$ stage AND propagated through $3^{rd}$ stage OR
Carry is generated in $1^{st}$ stage AND propagated through $2^{nd}$, $3^{rd}$ stage OR
Carry is generated in $0^{th}$ stage AND propagated through $1^{st}, 2^{nd}, 3^{rd}$stage OR
Initial carry $C_{0}$ is propagated through $0^{th}, 1^{st}, 2^{nd}, 3^{rd}$stage.
- $1$ AND & $1$ OR gate for $C1$
- $2$ AND & $1$ OR gate for $C2$
- $3$ AND & $1$ OR gate for $C3$
- $4$ AND & $1$ OR gate for $C4$
To implement the look-ahead carry generator, $10 \text{ AND & } 4 \text{ OR}$ gates are required.
Correct Answer: B.