Parallel binary addition (ripple/CLA context): Binary numbers can be added correctly in a basic parallel-adder circuit when ________.

Introduction / Context:
Parallel adders (ripple or carry look-ahead) implement binary addition bitwise with a carry chain. To add signed integers without extra hardware, digital systems typically encode negatives in 2's-complement, letting a single adder perform both + and − (as A + two's-complement(B)).

Given Data / Assumptions:

• Basic parallel adder with Cin/Cout between bit slices.
• Signed arithmetic desired on the same adder.
• No special correction stages unless using BCD.

Concept / Approach:
2's-complement provides a unique zero and identical addition hardware for signed add/sub. One's-complement introduces a negative zero and an end-around carry fix-up step. Grounding carries breaks addition. Simply “noting” negatives does nothing functionally.

Step-by-Step Solution:

Verification / Alternative check:
Instruction sets implement SUB as A + (~B + 1), i.e., addition of the 2's-complement of B.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing one's-complement bit inversion with full two's-complement (invert + 1).

Final Answer:
negative numbers are in 2's-complement form