The correct answer is (c), hard disk. A hard disk is a storage device that is used to store data permanently. It is a magnetic storage device that uses a rotating platter to store data. The platter is coated with a magnetic material, and data is stored on the platter by magnetizing tiny areas on the surface of the platter. Hard disks are typically used to store large amounts of data, such as operating systems, applications, and user files.
(a) Keyboard is an input device that is used to enter text into a computer. It is a flat, rectangular device with a set of keys that are used to type letters, numbers, and symbols.
(b) Mouse is an input device that is used to control the cursor on a computer screen. It is a small, handheld device with two or three buttons and a scroll wheel.
(d) Printer is an output device that is used to print text and images on paper. It is a machine that converts electronic data into a physical representation on paper.