Which operating system was originally developed by Bell Labs and supports multitasking and multiuser environments?

The operating system originally developed by Bell Labs that supports multitasking and multiuser environments is UNIX. First introduced in the late 1960s and further developed in the 1970s, UNIX was designed to be flexible and powerful, allowing multiple users to operate on the system simultaneously while effectively managing various processes. Its design principles influenced many subsequent operating systems, making it a cornerstone in the field of computer science.

Although other operating systems, such as Linux and Ubuntu, derive concepts from UNIX or are built upon its ideas, they are not the original development from Bell Labs. Windows, on the other hand, was developed by Microsoft and has a different architecture and user model that contrasts with UNIX’s design philosophy. Thus, acknowledging UNIX's historical significance and its capability to support advanced computing makes it the correct answer to the question posed.