What does a full-adder add in one operation? Choose the statement that correctly describes the inputs combined by a full-adder cell.

Introduction / Context:
The full-adder is the building block of multi-bit adders. Understanding exactly what each cell adds clarifies how n-bit adders are constructed by cascading these cells along a carry chain.

Given Data / Assumptions:

• A full-adder has inputs A, B (operand bits) and Cin (carry-in).
• Outputs are Sum and Cout (carry-out).

Concept / Approach:
Each full-adder processes a single bit from each of two operands plus the incoming carry from the previous lower-order bit. It does not directly add multi-bit numbers; instead, many full-adders in parallel handle different bit positions to realize multi-bit addition.

Step-by-Step Solution:
Identify operands: A and B are single-bit inputs.Include carry chain: Cin is the third input.Therefore, a full-adder adds two single bits and one carry bit at a time.

Verification / Alternative check:
Truth tables and gate-level schematics of a full-adder confirm three inputs and two outputs, with Cout feeding the next stage.

Why Other Options Are Wrong:

• Two 2-bit or two 4-bit numbers: These require multiple full-adders arranged in parallel, not a single cell.
• Two 2-bit numbers and one carry bit: Same issue; implies a multi-bit adder, not a single full-adder cell.

Common Pitfalls:

• Assuming the presence of multi-bit buses per cell; in reality each cell handles one bit position.
• Overlooking that Cin is an input, not an output.

Final Answer:
two single bits and one carry bit