Hi, Hee-Young Shin!
Hi, Abrita!
Hi, Devendra!
I am having the same issue in Firefox, so I tried Chrome. There is a tiny horizontal progress bar above the scratch area and the quiz. The scratch area does seem to complete loading but the quiz never does in either browser. My current refresh has been loading for the last ten minutes. Safari takes you to the Wolfram home page when the link to the calculus class is clicked or pasted, so there is no point discussing that.
(30 minutes later) CHROME MESSAGE: "Connection Lost
Unable to connect to www.wolframcloud.com.
You may want to check your internet connection."
There's nothing wrong with my connection because I'm streaming "Ms. Marple" right now, LOL!
I did what Abrita suggested earlier: cleared the cache, deleted quiz 10, restarted the browser. Still no success. Hope this information can help get to a resolution OR maybe it will just work later today :D.