Explanation:

A logic gate is an elementary building block of a digital circuit. It is a physical device that takes one or more binary inputs (representing $0$ or $1$) and produces a single binary output based on a specific logical function (e.g., AND, OR, NOT). These gates are implemented using electronic switches (like transistors) and are fundamental to all digital electronics, forming the basis of computers. Option (b) A type of circuit is correct. Option (a) A software is a set of instructions. Option (c) A special Cd is irrelevant. Option (d) A computer game is an application. These gates are the hardware foundation of computation.