When a comment is no longer useful, you should do which of the following?

A) Edit the comment.
B) Delete the comment.
C) Reply to the comment.
D) Reopen the comment.

When a comment is no longer useful, the best choice is to delete it so that it doesn't clutter up the conversation or provide outdated information. Editing the comment may not be appropriate if it completely changes the meaning of the original comment. Replying to the comment is also unnecessary if it no longer serves a purpose. Reopening the comment is not applicable in this scenario.