We're aware there is currently a slight technical issue with the quizzes when accessed on mobile.
Fortunately there is a workaround! The best thing to do is enable desktop mode on your mobile device browser.
To do so, click on the menu button at the top right of the browser and select the option Request Desktop Site.
Please give that a try and let us know how you get on.
However, this method may not always work. Your best option is to complete the quiz on a computer. It should work best there.