An operating system (OS) is system software that manages computer hardware and software resources and provides common services for computer programs.
Let's analyze the options:
(B) Android: This is a mobile operating system based on a modified version of the Linux kernel, developed by Google.
(C) Solaris: This is a Unix-based operating system originally developed by Sun Microsystems.
(D) Windows: This is a family of proprietary operating systems developed and marketed by Microsoft.
(A) Mozilla: This is not an operating system. The Mozilla Foundation is a non-profit organization that develops free software, most notably the Mozilla Firefox web browser.
Therefore, Mozilla is not an operating system.