The correct option is (d) To compare a set of variables or unknown numbers
The explanation: A comparator is a combinational circuit that takes two numbers as input in binary form and results whether one input is greater, lesser or equal to the other input. The purpose of a Digital Comparator is to compare a set of variables or unknown numbers, for example A (A1, A2, A3, …. An, etc) against that of a constant or unknown value such as B (B1, B2, B3, …. Bn, etc) and produce an output condition or flag depending upon the result of the comparison.