It should be a correct answer too.
A sentence can be marked as a question by the use of particle -kah.
It is always optional and is largely confined to writing and formal speech.
Thank you! Some people downvotes without letting comments. And thank you for having re-upvoted this comment. When they get bad votes, we have the impression they are wrong!
I have one more question. Is "Apakah yang dia baca" correct? Duolingo doesn't accept "Apakah yang..."