Digital Logic

Answer : B

Explanation :

We need an adder for every bit. So  we should need m full adders. A full adder adds a carry bit to two inputs and produces an output and a carry.
                 But the most significant bits can use a half adder, which differs from the full adder as in that it has no carry input, so we need m-1 full adders in m bit parllel adder.