Which of the following is a key function of a half-adder?

A half-adder is a fundamental digital circuit primarily used for the arithmetic operation of addition between two binary digits. Its main function is to take two single-bit binary inputs and produce two outputs: the sum and a carry. The sum output represents the result of adding the two input bits, while the carry output indicates whether there is a need to carry a value to the next higher bit when the two input bits result in a sum that exceeds the value of a single binary digit (i.e., when both input bits are 1).

Given this, the correct function attributed to a half-adder is adding two binary numbers, which is exactly what the answer specifies. The half-adder is foundational in combinational logic design and is often used in arithmetic logic units and other digital systems where binary addition is required.

In contrast, other options such as performing subtraction, combining multiple binary inputs, or converting binary to decimal are not capabilities of a half-adder. A half-adder does not handle subtraction or support more than two input lines directly; it is specifically designed for single-digit binary addition. It also does not perform conversion tasks, which would require a more complex circuit design.