Thanks for reply, Milo.
However, just two option only in forum setting.

My objective are control the user's access right to post the reply.In other word, I need a function to group the user and set the permission for them to access. For example, User in Group A can view and reply in title a, but users in Group B can view the title a only. The users form group B cannot post reply (Users in Group B are also registered users).

The access rights are list down in previous post.
Thanks for any suggestion or tips.