Tanwin
Name the sign at the end of a word: tanwin or a single vowel.
How this exercise works
A short sentence appears and the question names one of its words: you choose the sign at its end. If you choose wrongly, the exercise explains both signs, and the question comes back at the end of the round.
كِتَابٌ — كِتَابًا — كِتَابٍ