How do I require students to post to a course announcement before they see replies?
You can require students to post to an announcement before they can see replies.
In Course Navigation, click the Announcements link.
Click the Add Announcement button.
Type a title for the announcement in the topic title field  and add content in the Rich Content Editor . Click the Users must post before seeing replies checkbox .
Click the Save button.
View Announcement (Student View)
Once you add the Announcement, it will show up on the Announcements page. Students will not be able to see replies until they reply to the Announcement.