Which of the following is an example of a time-sharing operating system?

Concept

A time-sharing (multi-user) operating system lets many users interact with one computer at the same time by giving each a very short CPU time slice in rapid rotation. The fast switching makes every user feel as if they have the machine to themselves. The defining trait is concurrent interactive access by multiple users from separate terminals - not merely the ability to store more than one user account.

Application

Test each option against that defining trait - concurrent multi-user terminal access with CPU time-slicing:

• MS-DOS - single user, one task at a time; no concurrency or time-slicing.

• Windows 10 - supports multiple accounts, but the design serves one interactive desktop session; account creation is multi-user storage, not concurrent terminal time-sharing.

• macOS - same as above: multiple accounts are supported, yet the architecture targets a single interactive desktop user.

• UNIX - designed so many users at separate terminals share the CPU through rapid time slices simultaneously.

Result

Only UNIX matches the time-sharing definition (concurrent interactive multi-user access via CPU time-slicing). Having multiple user accounts, as in Windows 10 or macOS, is not the same as time-sharing, so UNIX is the correct choice.