Have you tried answers given here:
edit: Benjamin Ayinbuomwan
are you talking about this 'quiz' :
<strong> important text </strong>
<sub> subscripted text </sub>
Benjamin, please see if you have enough XP points to unlock it, it may not work if your XP points were less than what was needed to unlock correct answer.
Anyways, are you using SoloLearn mobile app or web? maybe restart the app/browser helps?