Which two statements are correct?

The user smith, whose primary group is smith, wants to create a file in his home directory, which
belongs to the group apps.
Which two statements are correct?

A.
SGID should be set on smith’s home directory to let smith create files that belong to a group
that is not his primary group.

B.
The user smith can create a file that belongs to the apps group, only If his private group is the
apps group as per /etc/group.

C.
The user smith can use the newgrp command to change the primary group to apps, only if
smith is listed in /etc/group as a member of the apps group.

D.
The user smith can use the newgrp command to change the primary group to apps, but a
password is required if smith is not listed in /etc/group as a member of the apps group.

Explanation: