By default, comments are disabled for announcements. When creating an announcement, you can allow replies to that announcement by selecting the Allow users to comment checkbox in the announcement options. Additionally, if an announcement allows users to reply, you can require students to post to the announcement before seeing other replies.
You can also allow or disallow comments after an announcement is posted.
Note: If announcement comments are disabled for your course, comment options may not be available to you. Check Course Settings if you cannot manage user replies in an announcement.
Click the Allow users to comment checkbox . You can also require students to reply to a post before seeing other replies .
Close in Announcements Page
To close an announcement for comments from the index page, locate the announcement. Click the Options icon  and click the Disallow Comments link .
To close more than one announcement for comments from the index page, click the checkbox next to each announcement  and click the Lock Reply button .
Open for Comments
To open an announcement for comments, locate the announcement and click the Options icon , then click the Allow Comments link .
To open more than one announcement for comments from the index page, click the checkbox next to each announcement  and click the Lock Reply button .
Close in Individual Announcement
To close comments within an individual announcement, click the name of the announcement.