Which command is used to add the user candidate to the group training in Samba 4?

The command to add the user "candidate" to the group "training" in Samba 4 is indeed the one that uses the samba-tool with "group addmembers". This command specifically targets the group management aspect of Samba Active Directory.

Using this command structure aligns with the conventions of managing users and groups in an Active Directory context. The samba-tool group addmembers command is designed to allow administrators to add one or more users to an existing group. By using "training" as the group and "candidate" as the user to be added, this command efficiently performs the required action.

The other options do not fit the correct context or syntax expected for adding users to groups in Samba 4. For instance, the samba-tool user addgroup command does not exist as an official command; instead, groups are managed separately. The samba-tool groupadd command is intended to create a new group rather than adding members to an existing one. Lastly, the samba-tool ad group modify command does provide functionality for modifying groups but is not written precisely for adding specific users as members in the straightforward manner required in this situation.

Thus, option B is the correct choice as it properly utilizes the appropriate command