Which statement about users and user groups is correct?

A single group can contain any number of user members; there is no one-user limit enforced by the Linux group model.

Linux systems routinely define dozens or hundreds of groups for system services, applications, and users; the count is unlimited.

Group membership is mandatory in Linux - every user must have a primary group, so belonging to no group at all is not possible.

Linux mandates that every user have a primary group, recorded as the GID field in /etc/passwd and defined in /etc/group. Even without explicit supplementary group membership, a user always belongs to their primary group, which is typically created automatically - often sharing the user's name - when the account is added.