Hi all! We are aware of the sound issue. It appears to be an issue with British Telecom. Hopefully it will be fixed soon.
If you turn off the sound options, the lesson shouldn't give you any questions that require sound to answer. To change your sound settings, hover the mouse over your username where it appears in the blue bar at the top of the screen (on desktop version). A menu will drop down. Click "Settings". From there, once you turn off your speakers, click the green "Save" button. That should make it so you can complete the lesson and move forward. :)