Explanation:

Ubuntu is a popular open-source Linux distribution, which means it is a complete operating system. It is designed for computers, smartphones, and network servers, providing a graphical user interface and a suite of applications, managing hardware and software resources. Therefore, option (a) is correct. Option (b), 'Programming languages,' refers to formal languages used to write computer programs (e.g., Python, C++), which Ubuntu is not. Option (c), 'Microprocessor,' refers to the central processing unit (CPU) of a computer, which is hardware, not software like Ubuntu. Option (d) is incorrect as Ubuntu is definitively an operating system.