Explanation:

The correct option is (B) microprocessor. The microprocessor, often referred to as the Central Processing Unit (CPU), is the 'brain' of the computer. It is responsible for executing instructions, performing calculations, and manipulating raw data into meaningful information. It fetches, decodes, executes, and writes back data, thus controlling the flow and transformation of information within the system. Option (A) keyboard and (D) mouse are input devices used to enter data into the computer. Option (C) monitor is an output device used to display information to the user. These devices facilitate interaction with the computer but do not perform the core data manipulation and control functions like a microprocessor.