I'm trying to complete the chatter section on Trailhead, and I'm getting the error "Challenge Not yet complete... here's what's wrong: 
No feed post was found that linked to the Trailhead URL.", and this doesn't make sense because I clearly posted the URL multiple times.

The criteria: Using the standard poll and link Chatter actions, create two posts to engage with the Chatter user community.
Create a poll post. Ask your users to rate their experience with Chatter and ask for feedback in comments.
Create a link post. Share a link with other users to http://developer.salesforce.com/trailhead - the best learning tool for Salesforce out there!